Were the reflector you used polished aluminum, or some sort of coating or paint? A lot of fixures use shiny reflectors now, most of them MIRO (See: http://www.alanod.com/opencms/sites/alanod.de/en/miro/Was_ist_MIROx/index.html
) which is a coating of aluminum on a base material. I know that you can get it in several thicknesses, perhaps you used the thineest one? I'd be interested in knowing the details of the problems you were having, as I try to use reflectored lamps, even with the cost premium, but will refrain from it if you have seen maintenance problems.
FWIW, a 28W T5 is about the equivialnt to a 32W T8. All T5's have the 80 series phospher (830, 835, 841, etc). They also, as a rule, are run with programmed start ballasts, which should give longer lamp life in frequently switched applications. The reason they are used with reflectors is that the smaller diameter requires a much smaller reflector than a T8 lamp. This makes it economical to use a reflector in the fixure. The T5HO's, while not as efficient, are a grat lamp if you need a lot of punch in a small package. Be careful with these, as different lengths have different lumens per foot. In other words, if you're washing a wall with a bunch of 4' fixures, and put a 3' fixure to finish the row, the brightness of that fixure will be different than the 4' fixures. (note, this is for the HO version only!)