What about the limited slip differential in the sport???
Re-selling a sport is easier as there are soooo many SE's about!
What colour are they??
That amount of extra miles on an IS means little or nothing at all!!
With the money you save by buying the sport you could get some nice tasty mods to start you off like exhaust, induction, tint for front windows, coilovers etc etc etc!!!
I would go for the sport!!!