Of the list of games you mentioned, Shift 2 never had many online players, and most players didn't bother doing tunes for Shift 2 for any mode, as most of the career milestones can be beaten using untuned cars, if you choose the right car. The only milestone that may not be possible is a 4 second drift at Ebisu's tight drift track. I haven't found any youtube videos showing a 4 second drift there.
Carbon's tuning is pretty much the same for every car (always max power, max rpm) except suspension setting for understeer / oversteer, and tuning transmission for top speed for the Z06, and perhaps drift tires for the Viper in drift mode. For Pro Street, many of the drag tunes are unusual. The fastest drag car in the game is a stage 4 Camaro SS, launched in 5th gear (by assigning a button to 5th gear) with the throttle floored, and with only one shift. Similar gear skipping tunes were done for other cars, like only using 2nd, 4th, and 5th for the Supra (need buttons assigned to 2nd and 4th gear). Undercover's tuning was similar for each car, most of the difference being the settings for drivetrain and engine.
I'm not aware of any NFS games where console players can go online with PC players.
