All of this means almost nothing unless the car in question has been set up correctly, the tires are worth a damn, and even if the car has a limited slip and which kind for that matter.
A rear engine car can be tuned to understeer even when adding power in a low speed corner so it's not a given that GT40s are tail swapping monsters. That's a certainty. It will take some time and a will to learn how to setup suspensions but this is not moon shot science and there are many sources that explain completely how this works.
Tires. There are only two decent 15 inch tires that I know of. Avon's and DOT radial Hoosiers slicks. (I include all the dot slicks in this category). Any attempt to run junk like BF Goodrich Comp TA/s hard will only result in round balls of grease attached to the wheels. ANY GT40 with quality summer only 17 inch tires on it will run ANY cobra into the track that runs cheepo 15 inch poser white letter junk tires on it. AND the more power the cobra has the quicker the rears will overheat and sooner it will get run down by the GT40. I don't care if the cobra has 800 hp and the GT40 has 300 it won't take more than 15-10 minutes on track before it's all over.
Setup. Once it is understood what is going on with sway bars, spring rates, shocks and their tuning, tire pressures and limited aero mods then a 1/2 dozen track days will go a long way towards really improving a ill handing car. A nice big flat area of blacktop should be used for a skidpad the first time a new car is past shakedown systems testing and is moved on to suspension setup evaluation.
You can't just put a kit car together and expect it handle well at the limit of tire adhesion. Frankly most kit cars builders will have no way to predict which direction the car will go the first time they floor it.
Limited Slip. OK here's my humble opinion. If you build one of these cars with more than 250hp then you are crazy if you don't equip it with a limited slip diff. I have Quaife TBD's in both of my cars, SLC and GT40, and they are absolutely magical. Both rear tires do the same thing no matter WHAT YOU DO! My GT40 was transformed from a wicked unloaded single tire burner to a nice predictable corner exit with the Quaife I had installed in the Renault it has in it. So much so that I had to tune the LOW speed push out of it.
Take a $1000 out of your engine budget and put it into a TBD. You will thank yourself later.
So which car type is faster...…………...the one that is correctly tuned on the best tires.
Here's two good books on suspension tuning. There are many others.
https://www.amazon.com/Chassis-Engi...=8-14&keywords=chassis+engineering+herb+adams
https://www.amazon.com/How-Make-You...preST=_SX218_BO1,204,203,200_QL40_&dpSrc=srch
One more:
https://www.amazon.com/Race-Enginee...preST=_SX218_BO1,204,203,200_QL40_&dpSrc=srch