Optiplex 745 Mini-Tower Graphics card

OK I got here on time, good.
Mini Tower is not that "huge" as you think. You can not fit just any video card. Watch this video first, all Optiplexes share about the same hardware architecture http://www.youtube.com/watch?v=tbVoe-4_oZ0
Unfortunately no card that is more than 7.5 inches long or 2 slots wide will PHYSICALLY FIT inside the case - it was found that only single bracket video card can fit due to BTX MOBO, where card internals facing upward towards PC internals, not ATX, where dual card design is blocking another PCI slot by facing downward.
If you prefer the card with beefier fan, then the length of the card must not exceed 7.5 inches, otherwise only "skinny" single bracket, single slot cards can physically fit.

Pictures below will prove my point.

View shows no room for dual bracket



Single bracket only, or you have to cut dual bracket in half



Here you can clearly see only single place for the bracket



Visual explanation



7.5 inches explained, also shown "obstacles"



This is the picture of actual "skinny" single slot video card (not sure which model)- perfect, "glove" fit.



So, I found 2 GDDR5 7750 cards (GDDR5 is better than GDDR3, even if GDD3 offers 2 GB RAM), which confirmed in reviews to fit Optiplex gx620, 745 and 755 cases (the difference between those models are different processors).

Skinny, flimsier in terms of construction, completely single slot XFX 7750 http://www.amazon.com/XFX-DisplayPort-PCI-Express-FX775AZNP4-FX-775A-ZNP4/dp/B007Z3T5JC
A bit beefier cooler, not as skinny, more durable in construction PowerColor AX7750 http://www.amazon.com/PowerColor-AX7750-1GBD5-DH-Video-Graphics/dp/B00775OC28/ref=sr_1_1?ie=UTF8&qid=1362783129&sr=8-1&keywords=AX7750+1GBD5-DH

I cannot say which one of those 2 is better, both are good and got less bad reviews related to structural build.
I saw recent recommendation regarding drivers "Changing to the just-released AMD catalyst 13.2 BETA driver improved performance noticeably in just about every game" posted 03/05/2013.

Next will follow maximum possible upgrade, 7750 is weaker...

So far I found only one 7770 video card which will fit inside - PowerColor AX7770 http://www.newegg.com/Product/Product.aspx?Item=N82E16814131477
HIS H777FN1G Radeon HD 7770 very tight fit, almost touching heatsink http://www.newegg.com/Product/Product.aspx?Item=N82E16814161433
From NVIDIA I see SPARKLE 700025 (SX650TI1024KD) GeForce GTX 650 Ti http://www.newegg.com/Product/Product.aspx?Item=N82E16814187200
7750 cards do not require power supply upgrade, 650 TI and 7770 are.
There are so many options available here so I would just recommend one of the good one CORSAIR CX500M (modular) http://www.newegg.com/Product/Product.aspx?Item=N82E16817139050 You need 500 watt at least, stronger is better depending on your money.

This is about it.