I would just look for one for sale complete or near complete.

Well-started GTM #300 Build with 98% of all needed parts and tons of upgradesFactory5forum

I'm not sure there's a way to measure the two cars against each other. Building and owning a GTM is going to be a much different experience than the Nissan. I looked at the GTM pretty closely because my wife wants one. No question it is a slick beast. I think it has maybe one awkward body line, but over-all it's beautiful. I think a decision like this is best made based on the type of experience you want.

Kit car.
It will be worth 10x more when you're done and will no depreciate much if at all.
And it's exotic looking.
There's a GTM at the cars and coffee I go to.
It was for sale and the guy was asking $70,000 US for it.

Thnx to u all for ur honest opinion, after thinking and debating i have realized that i like driving more than building, so am going to stick with the Z, i just cant let it go and building it will be quicker.

Maybe in the future when GTM V3 comes out ill build it after the Z.