Have been asked to get a full-suss bike for a mate as a surprise present, and think something like a Trek Fuel EX8/9 could be just the ticket. However, sizing seems very long in the TT department. Anyone have ideas as to what size would best fit someone 6'1"??

the one above a 17.5. 19.5?

heihei,
I've had one and two of my mates now have them. I'd suggest a 19.5" frame – their sizing is well confusing though, i think it's a 18.5 virtual and 19.5 actual.

The 17.5/18.5 will probably be too small – hope this helps.

They do a 15.5(virtual),17.5(virtual), 18.5(virtual), 19.5(virtual), and 21.5"(virtual). For 6'1" in my experience from working in a Trek dealers i'd guess 19.5", though it's always best to sit on a bike first…

I'm 6'1" and I've got a 18.5 virtual / 17.5 actual. I'm not sure if I should have got the size above though. The 18.5 virtual has a 24" effective top tube though so it's pretty long, as big or bigger than most other brands 'large' frames. For me it's ok with a 90mm stem, but if I'd gone a size up I'd have been able to comfortably run a shorter stem.

Had a fuel ex 8 2009, and ex9 2010 both in 20.5/21.5" (actual/virtual), I'm 6'4" and was perfect sizing for me. Therefore would guess A18.5"/V19.5".

As above though best to sit on and try the sizes first. ❗

I'm 6'2" and I have a 19.5(v) and it's perfect. Seat is high though so depends how you like em. But 19.5(v) is definately the right size.