Jeff Schewe is definitely the man when it comes to very large, very fine detail prints. Which has me wondering if you might get more feedback on Luminous Landscape forums.
Other people who come to mind are Keith Cooper over on Northlight-Images, and there's one more I am racking my brains to remember. I'll post it when it comes to me.
[EDIT] Vincent Oliver. He runs photo-i (now called photo-i & video-i). He used to be the go to man for printer information, and gets around the forums sometimes.