I can't say anything about new 1200's or, for that matter stock ones. I can say that the one the OL has is quick. It's about 40 pounds lighter than the America and has a lot of mid range torque.
Low end torque isn't significantly more than the America as determined by the amount of throttle and clutch slipping needed to climb the ramp into my little shop area. I think this is probably because of all the modifications on the engine.
Going through the gears, it is an effort to hang on with a lot of throttle, but it runs out early because it is geared lower than the old '76 Ironhead I used to have, so the top speed is no faster than the America, and maybe slightly less.
The ride is less than pleasent and it handles like a log, but that might be partly because it has been lowered a lot.
Oh, and it vibrates worse than the 500 Velocette single I had years ago.
Things I do know about the new ones is that they have 1 more gear, so they might have a more liberal top gear ratio.
The rubber engine mount seems to work, at least it does above 2300 rpms.
The new bikes weigh upward of 100 pounds more than they did in '88, so any power gains they may have made while refining the design are more than offset.
The engineering required to maintain proper drivebelt tension whilst the engine/gearbox assembly are flopping around on the rubber mount boggles the mind and makes the way the aircleaner moves next to the leg seem entirely against the ways of nature.
Untill they find a way to reduce the amount of rotating mass, HD performance is doomed to be less than expected.
