A few days ago my 3 year old son and I got out the SCX F1 Compact set, we had a blast. We set up the track on his small Thomas-the-Tank-Engine-type table. We could only set up a small oval but even with that set up it was evident that there were lots of difference between the F1's that came with the set and the Nascars. The first difference was that the Nascars seemed to slide much easier and didn't accelerate quite as quickly.
When I first got the F1 set I was impressed by the level of detail in the molding of the F1's. The finish on the McLaren is well done, the printing is good but the reddish bits of printing are a bit too low chromatically speaking... but that's nit picking to be sure.
The F1's have very sticky tires, much stickier than the Nascars. The grooves in the tires may have something to do with the cornering speed of the F1's. Piloting the McLaren, my son was able to pass me within a few laps of the start of the "race." The magnetic pull of the F1's seems to be stronger because they "snapped" down on the track. But with all their speed and ease of cornering, the F1's don't give you much warning when they're going to deslot. The 'Cars always start to slide a bit before letting go...the F1's are off like a shot!
I will be working on a full review of the F1 set soon.