No question in my mind I'd go fot he Nightster, the 1200 has loads more power than the 883 a much more fun bike to ride.
Nightsters are a better looking bike imo. Powerwise, with the conversion added in, I can't imaging there'd be a huge difference - and if getting the most powerful bike is a concern your're looking at the wrong range, and prolly the wrong brand...
I don't think the dealer fitted 1200 would void the warrranty. When I had my Iron (MAGIC bike!) after I'd fitted a tuner, Heavy Breather and SE pipes one of the mechanics at the dealership said once the 1200 was done nothing would catch it.
It's personal but I really like the minimalist look of the Iron.
Don't commit to anything before checking out the 48 though - that's the Nightster concept taken to its ultimate version. Stunner!
Was going to say sounded a bit rich but I'm guessing its the one at a dealer in Nerang on ebay? Looks like a nice bike, side mount plate, drag bars They are around $16500 ride away new.
The prices on bikesales.com.au aren't necessarily what they sell for, but don't be one of the numerous people that send a text msg offering half listed price....
Its hard to get money off Harley's, and Nighsters aren't that common. Worth a shot though, a dollar saved is a dollar earned.