No, the SSD will hold both my data and the OS. I also will be doing quite a bit of video/picture work, mainly 3DS Max and Maya. That's about the most taxing thing I do on my computer, and it's not everyday or all day long. I don't play games but the 3D work is probably the same as playing a game to an SSD (lots of reads/writes).
I'm more or less concerned with the lifespan of TLC memory at this point. I'd go with the 840 Pro 512GB I saw, but am concerned about its performance after several months (and the reliability, based on some reviews I've read about them failing after a few months of even light use). I haven't see anything on the Evo but that's because it's still new. The performance between the Evo and Pro is pretty much not noticable from what I've read and see in benchmark tests... The one test I did reference above about the TLC stress test does seem promising in that an SSD with TLC memory can last to around 10+ years even with moderate use.
IMHO the key to optimum ssd performance is understanding how TRIM and garbage collection interact and setting up the correct configuration. I wouldn't be concerned about the ssd life span as technology well make it obsolete before it wears out. EVO or PRO get's it done. The newest generation of ssd's are catching up with Samsungs controller technology. Prices are approaching .40 cents a gig.