If I bought this computer http://ncix.com/products/?sku=76683&...Entra%20series and than added AMD Radeon HD 7750 1GB how much fps would I get on highest and lowest settings?

should get about 60 on highest i think with a 7750

I hope you got a new power supply as well, otherwise you're just waiting to fry something.

Should be able to play most games on medium-high

Power supply is fine. I5-3450 max TDP is 95w's, and the max TDP of the HD 7760 is 52W's. Under full load 147w's+20-30w's for HD, DVD drive, and fans. That seasonic is a QUALITY PSU, one of the top 3 consumer brands offered on the market. It's 80+ Bronze certified and can easily handle an HD 7770, and POSSIBLY and HD 7850(cutting it close tho)

To answer the OP, I'd get an HD 7770 as they are about the same price but offers a bit better performance. If you want to get an HD 7750 make sure it's a 1GB GDDR5 not 2GB GDDR3. With earlier GPU you will effortlessly max out league, play games like D3, SC2, and WOW a mix of high-ultra settings @ 1080p. Games like Metro 2033 and Bf3 a mix of med-high(HD 7770) mostly med(HD 7750).

Guh, I'm out of the loop a bit more than I thought.

Are power draws really getting that low on gear these days?

Max power output of intel CPU's at stock speeds have gone down by alot. The one in that PC is actually 77w not 95w. The cards listed are lower powered cards with a max draw of 52 and 75-80ish. Cards like the HD 7950 and 7970 has much higher draws, but it's not like the GTX 480(mine has drawn 302w's once alone).