What's the bigger improvement?
 

Would I realize a better ET from a 50 hp N/A increase or a gear swap to 4.10s on my DOHC?

My advice: Your cobra NEEDS gears! They are horribly undergeared from the factory. Do the gears first, then the 50hp.

sounds good. thanks.

Go for the gears I just had some 4.10's installed in my GT...

For your snake I'd get 4.30's intstead of the 4.10's. The more gear the better for the 4V because it likes to rev.

I'd get the gears also, but your ET will get better only if you can hook up your tires, traction, traction, traction!! :)