4ft T8 lamps should be in the 2500 to 3000 lumen range. It sounds like you are quoting the "temperature" rating of the bulbs. Soft white are about 4100K, bright white are 5000K and daylight are 6500K bulbs. I just changed the two four tube fixtures in my kitchen to T8's with GE electronic ballasts yesterday evening. I used the daylight bulbs as they yield the best color rendition of what you are looking at. Probably was a mistake. The light starts out bluish, then goes nearly white as the bulbs warm up, but way too bright, even for my very dark kitchen (all wood, in a log house).
For a shop, 6500K bulbs would be great however.
Charles