Supposedly this was fixed in the last patch - it does seem to take less time to access your garage when you've got over 1000 cars. It is qucker than before, but occasionally it can still tkae between 3-5 minutes just for your favourites to appear.
BUT since the patch, a new problem has emerged, people keep getting 'stuck' in lounges and lobbys and can't get out. Especially annoying if you are doing a setup session for cars for a race series, only to wait 15-20 minutes upon 'exit', then loose the yellow connection light on your PS3 and have to reboot the game, loosing your setup you just spent maybe an hr or 2 creating.
So Polyphony has fixed one thing, but have created another problem.
Nice one Kaz - good to see your on the ball m8.