That's fine. Your GPU shouldn't use more than around 220W under load, leaving you with 210W for everything else. It's not ideal, but it'll do.
More importantly: what the heck are you doing with almost the most powerful CPU available and a crappy graphics card? Do you need CPU power for heavy processing or something?
The 2500k was a price performance leader and in my price range. I do a fair amount of video encoding and decoding and I wanted it to be somewhat future proof. At the time I thought I would just get buy with embedded graphics as I had heard the Intel 3000 hd graphics were decent. I have subsequently decided that I would like something better. The 6770 seems to pack a good punch for the price and I can use the stream processors to accelerate opencl enabled applications.
I'm quite concerned about stability. Will this card be pushing my system to the edge? If its a comfortable fit now will it give me room to upgrade in the future (add an ssd, another card maybe even)?
I looked at the eXtreme Power Supply Calculator(http://extreme.outervision.com/PSUEngine) and I don't know if my motherboard would qualify and a "High End - Desktop" motherboard or a "Regular - Desktop" motherboard? Also does a 7200 rpm sata drive qualify as "regular sata" or "high rpm"? Finally would the fans that came with my antec 300 case be "regular" or "high performance" fans
SSDs use virtually no power. Another card, on the other hand, would definitely need a more powerful PSU.
I didn't realize you weren't in this for gaming. In that case, the CPU/GPU sounds good. Now you need a better mobo. A P67 board will let you overclock the 2500K, which is a VERY good idea. You don't have to crazy with it to get a lot of free performance. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
It's got all the basic goodies (USB 3, Sata III), but it won't handle SLI/Xfire, PSU or no PSU, so think about whether that's in your future.