Yes it will cause a decent bottleneck 2.4ghz isn't going to be enough to push a gtx285 to its full potential. In my opinion don't waste money on a new system keep your current system and just add a gtx275 it wont be bottlenecked as much and wont cost you a lot, not to mention give great performance slightly less then gtx285. What resolution do you play at? at higher resolution your graphic card tends to do more work so if your play at high resolution you wont have much of a bottleneck.
Here is some benchmarks with my system
I have q6600 3200GHz & GTX295 and in farcry2 benchmark I get:
81fps 1920x1200 4xAA ultrahigh setting -- with 3200GHz
81fps 1920x1200 4xAA ultrahigh setting -- with 3420GHz
exactly the same fps!!!
+1 for strangestranger. you asked for other options....have you considered upgrading your MB? If you swap out for a MB you can OC (you can find decent deals on newegg for about $100), you could get at least a gtx 260 or 4870 for a total of about what you would spend on the gtx 285 alone. This would give you the best of both worlds, a faster processor speed, and faster graphics. If in the future you decide you need more power you'll have cheap upgrade paths by adding a faster 775 processor and/or sli/crossfire for the graphics after prices have fallen even farther.