Remember, these things are a full 24" wide. Even 2byX joists or trusses only have 22.5" clear between them. The diffused lenses are designed to reduce lamp image for office buildings, not shops. They will reduce light output by ~15% alone over a bare bulb and the lenses will also fill with dust eventually, reducing light output even more.
No matter what fixture, I would be concerned about overall coverage and shadows. You should consider 9 fixtures (3 rows of 3) pushed further out to the corners (2' from wall) so there is plenty of coverage coming from all corners, reflecting off the walls into the middle to avoid a huge shadow, esp. with a car on the hoist.
What about strip fixtures? Do you really think you're going to need to get a car within 4" of a 12' ceiling on a regular basis?
(Don't ever buy big box store strip fixtures, the ballasts will all burn out within 1-2 years.)
Consider these:
They are lensed, but don't diffuse as hard as an "office" fixture, and have some gasketing to keep the dust out.
2L gasketed for $79
http://www.goodmart.com/products/1248624.htm
3-lamp gasketed for $85
http://www.goodmart.com/products/1184914.htm
I would consider (9) 2L strip fixtures to be the
minimum watts you would be happy with. For an extra $6 ea. go for the 3-lamps.
(thinking more)
In my state, 1watt/ft² is code minumum for an office, 1.4 for a workshop
(9) 58w (net) 2-32w fixtures in your shop is only 0.9w/ft²
(9) 87w (net) 3-32w fixtures in your shop is 1.35w/ft² PERFECT!
Oh yeah, do two switch legs- 5 on one, 4 on the other so you can tone it down when your not workin' too hard.
