So last night I endured the 15 minute phone conversation with a Comcast rep to sign up for "Game Invasion", which includes the 8Mbps download speed "upgrade". I didn't have the heart to tell the rep that I couldn't care less about all their games. I just wanted more bandwidth, something that I couldn't seem to find Comcast offering in any way other than "Game Invasion".
The cool thing is that (they claim) I'll pay $29.95 for the next three months, rather than the $42.95 they normally charge for the 6Mbps. After that it'll go up to $52.95/month.
If I'm not seeing better performance after 3 months, I can always go back to "standard" service.
So far in my speed tests, I've only come close to the 8Mpbs download rate once. However, I appear to appear to have more downstream bandwidth than before, where their claimed 6Mpbs rarely got above 4Mbps.
In addtion, my uploads are consistently at 700Kbps, which makes me happy.