Choppy 4870

Hello,

I just got a new system yesterday:
CPU: Phenom 2 940 (3.0GHz quad core)
Mobo: Gigabyte GA-MA790X-UD4
GPU: Sapphire Radeon HD4870 1GB Toxic
RAM: A-DATA 4GB CL5
HDD: Samsung 500GB 16MB buffer Sata 2
PSU: Enermax Pro82+ 625W
OS: Vista x64

The system works fine, but when I run games I get "choppy frame rates", like the ground will move choppily every few seconds when I move.

This is like a bad re-run, I had a similar problem on my old system with it's GF 7600GS.
This is driving me insane.

I'm still using a CRT monitor (from 2003), an LG 700P.

The OS install is fresh, not even a day old, and I'm using the latest drivers from the AMD ATI site.

Any ideas?

Games: Halo PC, UT3, HL2, L4D, CoD5, FC2.

AA setting is 4x for the newer titles.
I don't think the HDD is active during chops.

I don't think L4D and UT3 chopped on me when I ran them on my older PC at 25-30fps.
This seems to be consistent with the way Halo PC started chopping after I got a new system 2 years ago, again, it ran at 25fps on my old 2003 build.

I'm starting to think it's this LG 700P CRT monitor... I'll hook up a crappy 1024x768 LCD I have lying around here and see what happens.

Just tried it with and LCD (vga connector) and displays the same damn thing.

What the hell is this?

Let me explain this further, when I walk around and look at the ground, every few seconds it chops, like it's losing a few frames and fast forwards to them... something like that.
How the hell do I get the same damn thing on two totally different PCs is beyond me.

Both offline and online.

3DMark05 results: [url=http://service.futuremark.com/resultAnalyzer.action?resultId=4749070&resultType=12][/url]

3DMark06 score: 14808