I don't recall where I read it, but I'm almost positive I read of a comparison between a 1970 and one of the new SRT8's (may have been a 2008 model) done a couple of years ago when the new Challengers started rolling out the door. In that test, the 70 was the winner, but only barely. Don't remember if the 70 was a manual or not, but if the test involved a 2008 model (auto only), that could make a difference.
As for the top speed, that's merely a function of gearing. The old 4-spd has a gear ratio of 1:1 in 4th gear. The new 6-spd has a gear ratio of 0.5:1 in 6th gear (or so I read). Of course this doesn't even consider the differential gear ratio in the rear axle.
Don't get me wrong, I absolutely love my new Challenger, and I've never even seen a 1970 Hemi Challenger except in pics. I just think it would be interesting to see a test done with stock vs stock, hemi vs hemi, manual vs manual, 1970 vs new.
Wish I had the references to back up what I'm saying. I'll look around and see if I can find a source or two. Now I'm even more curious.
But hey, I've been wrong before...