Magic Mouse tracking speed

I'm wanting to use the Magic Mouse but the fastest tracking speed in Preferences isn't quite fast enough for me. I've seen other posts saying to use the Terminal and enter this code:

defaults write -g com.apple.mouse.scaling 5

Then restart the computer.

It makes no difference what number I use instead of the "5", no change up through 55. Entering 99 made it go berserk.

I just ordered a new iMac, the bigger desktop model, which will arrive in a few days. I'd like to wean off my $10 Logitech mouse and use the cool-looking Magic Mouse, but so far the cheapo Logitech works better.

Any ideas?