My 04 Coupe is great on long trips and I'm going to guess that the G37 is even better!!
I've driven several (short test drives) and find them very comfortable.
However, the sports seats are a bit snug for me but I do like the ones in the coupe better than the sedan...again, just me..

I also use carsdirect.com when comparing vehicles and looking at target prices.
In addition to comparing to slightly used cars.
(several months ago, I test drove an 08 G37S coupe with 12K miles in like new condition. They were asking $24,500)