Well when I first started out I had 4 x 96watt PC and I was able to keep some acros, and three clams (on the sand bed). I never lost any corals.
Now I have 2 x 250watt halides over the same tank. (55gallon)
My corals and clams never browned or showed signs of poor polyp extension whatsoever.
I mean it is not recommended to keep clams under anything but halides, (not sure about T5's). I guess it all depends on the clam or placement in the tank.
the only thing that really did bug me with the clams was that growth was really slow with the compacts. with the halides I get a new scute almost every couple of weeks.
Even so I would hate for you to spend money on a clam and have it die due to lack of lighting. BTW what type of lighting do you have?
I still have the compacts in a box, they just need new bulbs. The bulbs are about 9 months old.