I'm playing the Steam version, and I can't figure out how to play without signing in to the Social Club. You can create a shortcut to the LaunchGTAIV executable and play without starting Steam, however. One less app to be running while you are playing.
Beyond that, I've had pretty good luck with the game on my system. I used the -norestrictions command line and was able to run at high texture settings with little performance hit over medium. The only thing is that the settings don't seem to want to save. Every time I start the game there are new graphical settings. I don't know if that's because the command line screws up the autoconfigure or what.