Actually, on that note, I will say that my GT5 garage was well over 1000 cars. Why was that? Well, thanks to having to rely on sheer luck to get a chance to drive the 800+ Standards, I would buy up any car I didn't already own, in case it would be needed later for whatever reason (or if it had a colour I particularly enjoyed - thanks, bizarre paint system). Thanks to them also usually being high mileage, permanently weaker versions, I'd also buy duplicates if I found a rare low mileage example. Most of this was before the OCD, but even with that added, you still had to rely on PD picking a handful of cars. It took ages for me to find the Nardo, for example.
My FM4 garage? It's hovered around 530-540 for a while. When it hits the latter, I usually sell off or auction a few cars that I rarely use, but I do have duplicates in that garage too. I've got about five NA Miatas (ironically enough), because FM4's awesome diversity in modifications has me wanting a few very different cars, and I'd rather have them available in the garage when I want, than shuffling through various designs and tunes to load on a single Miata. I've got my good old D350 blue car (with a GT1 RM look, and the most-used car in the FPM garage), another GT1-looking car at E275, a road-going bigger-displacement nat-asp black car at C425, a wickedly fast 13B-powered blue car in A600, and an Autocross-loving S700 13B machine too. They've all got slightly different focuses, all look very different, and are actually driven.