Depends. If it were the older Z06, with the crappy Goodyear tires, I'd give the edge to the Z/28. The Z06 would certainly outpace it in acceleration, but the Z/28 would be able to brake later going into corners and carry more speed through. I don't think the 'Vette's straightline speed would be enough to compensate for those shite Goodyear Eagle F1s.
3 seconds is huge, even on a track as long as the N'Ring. In a head-to-head race, that's an ass-whooping. Wholesale slaughter. It may not seem like much over a span of 7+ minutes, but think about the distance that would be between the first car crossing the finishline, and the second car coming in 3secs later. Conventional wisdom says that every 10th of a second is about equal to a car length. Let's say that's around 15ft. Using that, the distance between the 1st and 2nd car would be some 450ft. About a football field and a half, for Americans like myself.
And it's not just the rain, but the overall conditions and the car itself. Though it was only raining on one section, it looked like a pretty cold day, and a cold track is already a strike against any car riding on R-compound tires. Honestly, it's amazing the thing didn't spin out or slide into the grass(or a wall), even before the wet parts.