Ok, I got the same stutters that you're describing, in a ramp start, the PC loads the textures when I look around then it's gone, and I think, you could have it even with a very high end PC, I would be surprised if you were getting bad FPS with that CPU/GPU, my core i3 is in the same scale, but I can't oc it, at 4Ghz you beat me easily, plus you have a nice graphic card, I dunno what's your PC screen but you should have something smooth and nice. Personally I'm med/high settings, I hit 45 FPS average, that's enough for me, but I'm running a 19" screen though.
About the quantity of RAM, I think buying 16GB is an overkill to play, if you're encoding vids, using a ramdisk or softwares like 3DSMax, it can be useful. The frequency is more important... 8GB is enough.
The sound card should be really helpful, I'm looking to buy one. Tell us the result!!