So basically I can get near ingame quality and maintain 30mb per 1minute @ 800x600
Here's the site that I followed:
http://toxik.no-ip.info/x264/guide.html
Be warned, this is for those who are familiar with video encoding, it has several complex steps and requires lots of testing to reach the results that suit you.
When you get to the point where you've figured out how it works and can successfully encode an .avi into .mp4, dont use the quality settings in that guide, they're not for the source engine.
Use all default, with encoding at constant quantizers single pass, quantizer at 27.
Start there then mess with deblocking, b-frames and interlacing to fine tune.
EDIT*
Forgot to mention that I edit with premier pro 1.5, to use x264 you need export movie -> download debugmode frameserve:
http://www.debugmode.com/frameserver/ and use that, what it does is creates a small .avi file and acts as a middle man between premier pro and for example virtual dub (which x264 hates so dont use vdub with it.) it acts like a server for your frames that third party programs can encode off of, maintain lossless quality from premier pro and preserve all your editing. You'll also need to export your audio manually for muxing, /overwhelming. lol.