OR just use existing car knowloedge you have in your head. Although it's relatively pointless, seeing as the dyno numbers on stock cars are about as far off as they can get...To sum all of this up:
When you get a sponsor you get a free car. Go do the URL races first, that way you have more selection for that free car. If you don't take the free carand you make it to your 2nd sponsor, and you still haven't picked out a car, that means you get to pick 2 free cars in total. I STRONGLY recommend getting an SUV for your first sponsor. SUV race completion is needed for 100% completion. After stage 2 or stage 4 etc. those races are no longer appearing on the map and therefor have to be beaten on the "World Map" selection when you jump to your garage. Some of them you have to beat twice to get reputation and cash. If you're 5 seconds ahead however in the first race you usually dont have to do it again. In total you can get 5 free cars (I think), all of which can be saved for the very end to be chosen. I recommend that except for the SUV part, as those should be completed as you do the regular ones too. You have to switch to SUV and then drive to the areas. Anymore questions, just PM me or something.