The way I look at these these lap times I think that the differences between the CS and its non CSS competitors are so small that it boils to the driver's skills.
The same is probably true of GT3 vs GT3 RS 911, only a highly skilled driver will exploit the addition capabilities of the GT3 RS but it doesn't take away from the superiority and desirability of the car.
Yes probably. Interestingly enough, looking at GT3/GT3RS lap times they are so close (only couple of tenths per minute) that you wonder where all that RS superiority has gone but at least there you don't have to sacrifice two rear seats as they don't exist even on the standard GT3, lol.
You know actually, for the majority it won't ever matter if the CS matches 95% or 99% the performance of the CSS with merely a set of PSC2 and a re-map (correction: a reversion to stock map

) at ~310ps. The CSS is still the one which is the official record holder and a 400 unit limited edition. These two alone can ensure desirability remains high.
For the rest of us that are interested in actual technical differences, lap times and how/whether they are affected and by which items in particular, and do take our cars to the track it is a different story. Not going to bother with anything other than a set of Michelins and a map "correction" as the car just feels perfect to throw around bends at any speed I fancy (first car of mine that will every stay with 100% stock suspension) but I am pretty sure a few CS owners will be going down the CSS road, and maybe even further.