I did some back to back running last week and the Renault was faster by about 1/10 second over a seven-second or so lap. That's without any magnets of course.
Much as I hate to admit it, I found the Toyota not the quickest of the McLaren and Williams when I did a similar exercise months ago. Hard to be too exact with only one of each car, but my feeling is the McLaren is the best handling. The two types of tyre muddy the issue a bit.
Interestingly, the magentless Carrera Ferrari is almost as quick, but the SCX Minardi is faster! The SCX car is light (no scales sensitive enough so can't confirm this) and has a wider rear track. That makes it look wrong, but obviously pays dividends on lap times.
Going back to the Renault, I'd say the modelling is better than on any of the other three recent Hornby F1 cars. I'm not intimately familiar with the compound curvature of the real thing, but where as the others achieve their life-likeness through the great livery application, the Renault seems less slab sided.
Of course, I could be spending too much time contemplating the shape of toy cars.
Scott