All things being equal I can't see how the CSS can't be significantly quicker than the CS seeing as they went to a lot of effort for the 'ring record. Did the CS set a time?
I know the 'ring is a unique circuit as it's bumpy and twisty but more negative camber, better power to weight ratio and more effective brakes should help on faster circuits too.
Auto Express test against CTR would be interesting as CS was beaten by it a few months back, will CSS be any better?
Well the CSS should be quicker but I mean I'd like to see just how much on a track, driven merely by enthusiasts. When you say equal I imagine you mean same PSC2 tyres (which are not standard on the CS) and VW's deliberate CS detune ditched and a healthy 300-310ps available? Hmm... I don't think there'd be that much but I may just have the chance to find out at some point

Reason I believe this is how similar the cars are (basically the CSS "sits" by 90%+ on an already great CS chassis and setup) and that German motorsport magazines have already published some rather interesting lap times about the CS. Conclusion was that when on the same tyres as the CSS (Michelin Pilot Sport Cup 2) it seems it's not as slow as AutoExpress tried to present it (for whatever reasons). You have to remember that test (if you can call that a test) was done on stock Bridgestones and it woudn't surprise me if it was even worse than 2.5" as they are
that bad a tyre for sports driving. Definitely not representative of the car's potential. But change to MPSC2 (as in the CSS) or even MPSS and here's what happens:
Hockenheimring:
CSS: 1:13,1
CS (on MPSC2): 1:14,2
Cupra: 1:14,7
CTR: 1:15:9
Nordschleife done by Auto Motor und Sport reviewers:
CSS: 07:58
CS (on MPSC2): 08:07
Cupra: 08:14
CTR: 08:15