Codeman00, oh man you have to try the 14K Hamilton 175W MH. To die for, especially with Actinic supplementation. Don't give up on your 175W'ers yet. Look I still have my 14K's & could ground ship them to you, but I would need them back when I sell the fixture. PM me if interested.
Dawn/Dusk with T5 (2 bulbs) I have not found any problems. In fact they were the same bulbs that came from my other fixture. Your 175W vs 250W question depends on a number of factors.
-What the heck are you trying to grow
-How tall is your tank
-How far will the fixtures be from the surface of tank
-How long will you leave lights on
I'll give you an example:
User1: 250W MH 20K, 1 foot from surface, 24" height tank, only leave MH on for 5 hrs.
User2: 175W MH 14K, on top of tank, 20" tank height, 8hrs/day.
User 2 will have the advantage. I think for you're case it's not about 175W bulb, it's about not finding the right bulb. Please look into the 14K Hamilton, you will not be disappointed.