So In THEORY..would it not have been cheaper to go with 36 4' T5HO Bulbs & Fixtures?
Using the quick n dirty Lithonia @ Home Depot Example (FIXTURES ONLY):
T8: 72 Bulbs = 36 Fixtures (Assuming 2 per strip) @ 28.97 = 1050.00
T5HO: 36 Bulbs = 18 Fixtures @ 39.97 = 720.00
When you're installing fixtures that need to be consistent with rest of the building and you're paying labor, it makes sense to use new ones, so with what you're describing, I wouldn't waste money on new fixtures seeing that you're going to use them maybe 1,000 hours a year. It's worth the money to get sealed fixtures that can be dusted or wiped down easily if it's a sanding shop.
I don't know what the ceiling looks like, but painting it white using eggshell paint (not too glossy, but acceptable cleanability) makes a big difference.
ElectricLight brought up the point about glare on a 10' cieling...thats something I'd like more info on (Real world input from people with T5HO's in this application)...
I remember back when I had time and I sat down and crunched the numbers from info I got from various posts here that I needed 24 4' T8 bulbs in my parking end of the shop to get the light I needed... If I go with T5's I can go with 12 bulbs, 6 fixtures.. Acording to the MATH, cheaper & easier to install the less T5HO fixtures...which is why I was drifting towards the feeling that in TODAYS enviroment T5HO's are better bang for the buck..
Basic software that calculate fc level don't show you the consistency. If the ceiling is 10m x 10m and I light it up with a 1000 lumen flash light, the light level averaged is 10 LUX. That's because you know there's 1000 lumens and the ceiling is 100 square meter, which comes out to 10 lux per square meter. Realistically, you'll have a bull's eye in the middle and dark all the way around and totally unusable as lighting. This is an extreme example, but when you use fewer fixtures, there's a greater tendency for hot spots. As the ceiling height increases or beam angle increases, the hot spot becomes less and less intense and more even.
^ ^ Good advice for the ceiling height consideration. Research using "high bay" if you have over 15 ft ceilings.
Think about it more in terms of line of sight.
I've been paying close attention to lighting when I go to basketball games at area high school gyms, and all old school MH (metal halide) lamps are gone. Predominant fixture is 4 or 5 bulb T5HO hung consistently across the upper ceiling. Have not noticed any retrofit LED lights, but now there are some on market at considerable price.
You don't see the lamps directly in a gym unless you intentionally try.
BRAND NEW out of package metal halide and T5HO are not far apart in LM/W. The huge savings come from the fact that metal halide lamps degrade more than just about everything else out there. The output of TH5O allow them to fit in place of HID fixtures with a reasonable quantity of lamps. So, MHs need to make about double the lumens initially to stay within acceptable levels for the entire useful life over thousands of hours of use.
The worst in degradation performance is metal halide. LEDs and CFLs are not that far behind. Tube fluorescent is a distant third.
OP. you'll need to "Filter" the responses from Electric_Light as he won't give you any alternative from LED technology. He's 100% fluorescent only.
It sounds like Spudland_Dave will put such few hours on it that it that it makes no difference in a practical sense and he's more concerned with the cost upfront. If he use them 12 hours a day every saturday/sunday, it's just a tad bit shy of 1,200 hours. He should probably set them up for two modes.
One setting with 2 to 4 lamps left on (using 60 to 120w), but evenly spread out for every day use, and all of them on for working.
I could not care less here if he uses light sabres, fluorescent lamps, LEDs, nuclear isotope lamps or whatever.
Ballast/driver interference with other RF devices is concern for both technologies so buyer beware.
They can, but the technology commercialized for LED drivers is naturally worse, because they modulate differently. fluorescent lamps don't do hard switched PWM to the lamps. LEDs do. LEDs are especially known for jamming garage door openers if they're too close to it.
Ok, so feel free to punch holes in my theory/statement/understanding here...but I THOUGHT and understood that High Bay really meant (To over simplify here) Chrome Reflectors were on the fixture. And T5HO in a "Plain white" non reflector equipped strip fixture was OK on a 10' cieling.
The actual ceiling height doesn't matter, but higher ceiling keeps the lamps from falling within your line of sight. Your local Home Depot might have strip T8s as well as T5HOs on display. The glare level of having T5HO in line of sight is quite obvious. T8 isn't particularly pleasant to stare into either. If you're comfortable with the glare level of T5HOs, go for it.
The store itself is probably lit with T5HOs, but they're so far up that you only see the sides (past the cut off). You will see the glare if you consciously look up.
You have probably seen a frosted white round light bulb that's about as big as a baby's head. The purpose is to make it less bright, so the lumen output is evenly and smoothly spread across the entire surface so it's visually comfortable.
If you took the modest amount of out of pocket funds out of the equation, which would you buy? Pure, simple, which would you prefer if the small difference in price was not a consideration.
If you had a choice between a 1000 page and 2000 page toner cartridge that perform the same and you only print a few pages a week. Which would you buy? If price was no factor, everyone would buy the latter. He asked a realistic question. He already knows he's only going to use them lightly. If the first was $50 and second was $60, the first one is still a better deal for someone who seldom use the printer.
combined with my complete distaste to stand on my scaffolding every year to clean the covers..lets be honest, it wont happen...As it stands now in my basement workshop, when I replace bunt bulbs theres so much burnt on dust I need brake-cleaner to cut the grime off em 
but in the context of the question...I want to give all currently available & realistic solutions a shot here. We ALL know LED is coming into its own...may not be here TODAY in a form we want but its coming...
My Model Workshop in my basement is lit with 6500k Daylight bulbs..never measured the room or the lighting, but Its VERY Well lit. especially over my benches.