Well, I went to watch testing at Silverstone a few weeks ago. They were using massive amounts of traction control; even in faster (aero) corners like exiting Becketts they had quite a lot of TC.
Coming out of Luffield they were still on the TC a LONG way after McLaren, Renault and BAR. Another thing I THINK I noticed was that the other cars still seemed to be "moving forward" when using TC, but the Williams did not seem to be making forward progress. Red Bull, for example, was using TC - but it did not seem to compromise the acceleration as much.
The only car with worse traction (IMO)? Jordan..............
I have no way of telling how good their aero is.
But, the way I am interpreting what I saw and heard is this: a slow corner is a corner that you spend a lot of TIME in, also the rate of acceleration from a slow speed is greater than from high speed, so any traction problems must surely compromise the whole lap time more than a tiny aero gain in a corner that you whizz through in fractions of a second.
Also, worth noting that the McLaren and BAR gearboxes seemed to have much crisper gearchanges.
There you have my humble opinion on the subject.........