Well that should be good for a 1:50 or so online.

This difference in physics is horrid.
From practicing both online and offline today, I actually managed similar times after adjusting the setup.
It's starting to become known that a few settings react backwards to what you would expect in real life, specifically ride height and spring settings. You would think a lower front would put more weight on the front wheels promoting oversteer, but it seems to be the opposite.
Offline I was running 15 points lower in the rear than the front and the car was nicely neutral, with very slight lift-off oversteer perfect for turn-in.
Online, I'm running only 5 points lower in the rear, and took the rear toe from -0.05 to 0.00.
Fastest offline lap: 1'47.800
Fastest online lap: 1'47.9xx (can't exactly remember as it was a clean air mid race lap).
Fastest online lap w/draft: 1'47.488 (thanks for the tow EL_ZISSOU

)
I'll post up my settings later, PS3 is off right now. It's basically Turbo's settings, but with the ride height at -5 front, -20 rear for offline, and -10 front, -15 rear for online (plus the above toe setting change).