Probably skewed towards the superior power/weight of the Cobra, but we can address this with some real-life data:
Road America is unchanged in it's layout from "then" until "now", and we have stop-watches:
Pole time in 1965 for a 289 Cobra with a pro driver on ye-olde tires was 2:38 and change.
I've seen a decently-well driven NA1/2 NSX turn a lap on the same layout (with the kink) in the low 2:5X range, let's say a real pro driver (maybe ask Peter Cunningham what his PB is around there in a stock-ish NSX?) could get into the 2:40s with skill alone.
Not a pretty picture for the stock-ish NSX once you put that 289 on modern tires and/or look at the 427 version.
Anecdotally I think the skill cap for being fast in a Cobra is higher (basically have to be a little insane) where the NSX is easier to drive up to 8/10ths. So a novice/intermediate skill driver might be quicker in the NSX, but in absolute terms, the Cobra is going to take it barring more serious mods to the NSX. I've autocrossed against some well-driven kit Cobras and the power/weight "argument" is pretty convincing given the skill to take advantage.
NC1 NSX is a bit of a different story I think though in case that was the context.