I would say this regardless of how big you are - get the 1200, you wont regret it. A Nightster is basically the same bike as the Iron anyways.

But honestly, consider a Wide Glide or Street Bob. Im 6'1'' almost 200 lbs and sometimes I feel like a giant on my Nighster. Plus as others have mentioned, you can bottom out the shocks pretty easily. When I hit bumps while turning, my boots and pegs and sometimes exhaust scrap the ground, it can be pretty dangerous IMO.

If you can rent the Dyna and Iron both for an entire day each and see what one you like more.

 

The stock shocks suck for anybody over about 150lbs. I put 12" Progressive 412 HD's on my 48 and it rides so much better in the back now. No bottoming out and I'm 285lbs. Now I need to re-spring the front since it is noticeably more crappy than the rear now. I'll probably put the Ricor Intiminators in the forks as well when I re-spring it with Works dual rate fork springs.

http://www.worksperformance.com/html/home.html

http://store.ricorshocks.com/

 

I'm 6'2" and 275 lbs. I have an 06 XL883L that was wrecked, the front end trashed. Put forward controls and 16" apes with 2" risers on the little monster ( along with all the other repairs and upgrades) and have a sweet bike. Went from Savannah, GA to Daytona for Bike Week 2012 and we did just fine. I wish she had a bit more engine to compensate for the lower power-to-fattness ratio, but hey, she's paid for and I'm havin a blast runnin with my buds that are on 88s and 96s. Have fun brother.

 

I'm 6'2 190. I put 14" bars and forwards and I'm loving it. It might not be as fast as the 1200's but it takes me every where they can go. Like everyone else (Well most) said, It's your ride, don't get what everyone else wants. Get what you want and enjoy the ride.

 

An iron with some bars like the one above looks money! If you like it, ride it. That stigma that sporty's are chick bikes is bullshit. From a size (as in the dude) does play into it, but with seats and bars being replaced, it will work. I love them and thinking of getting one in a year or so

 

I'm 6'0 and 210. I bought my iron mid september. Rode it, loved it! It already had forward controls, and mini apes. Yea, I'm already considering a 1200 convo, but all I've got are slip-ons, so I'm gonna do stage 1 ac and tuner first. It's a fun bike to ride, and to be honest, the only time I notice it's an 883, is when I'm 2 up goin up a hill. This chick bike sh#t, eff that. Mine looks sick! My ole lady's dad was like you don't want a harley, you'll want something with more power, people with harley's are always gettin em worked on, blah, blah, blah! Piont is, anytime I've got my iron at his house I catch him sittin on it! Let him ride it once. He rides a Honda vtx1300. You tell me, what's up!