As many have said here, the lap is in the rain. Really, what do you want?
Additionally, keep in mind that the Z/28 and ZL1 will probably show less difference on this track than, say, Laguna. Nordschleiffe tests the car's cornering abilility and overall stamina to be sure, but there are also times where the Z/28 is just out-muscled on the straights by the LSA's horsepower. Now, get it into a windier track where it can stretch its legs and take advantage of the Trofeos, I think it'll get ugly.
Just my $0.02. YMMV.... but I'll bet that this car will be beating the ZL1 by the same margin on tracks that are a third of the length. Both are great cars, just depends on if you want the track-rat or the supercharged beast with a little more straight-line wallop.
'88 IROC-Z vert (14.9 @ 92.3) //
'10 2SS/RS LS3 - 423 RWHP, 418 RWTQ