As Carlos says, scale is elastic with regard to toy cars. I buy mine from e-bay, so if they turn out to be monstrously oversized or otherwise unsuitable, I put them back up for auction, so not much lost that way.
Don't worry about treading over previously covered ground too much either. If it was something that had been covered on the first two pages of the board, then I'd expect you to post on that thread, but otherwise I don't expect anyone to go trawling back into the depths to check if something's been covered before. People come and people go and there are always new arguments to be made or new points of view to consider. Worse thing that can happen is that I'm forced to merge two similar topics and I'd rather do that than someone not get full enjoyment from the forum because they were worried about upsetting the mods.
There are no dumb questions but you'll get plenty of dumb answers
