As far as Triban 3 measurements go - I'm 5' 9" and the 54 inch frame was just right for me with a bit of adjustment either way.
Being somewhat new to road biking I bought a shlightly shorter stem and flipped it and am gradually raising my saddle as I get used to the feel of the bike.
They are a shedload of bike for the money and are selling like hot-cakes. Chances are a few will drop by the wayside in the coming year and start showing up on
eBay etc? Not sure I would buy one used though when a new one is so cheap. This months 'Cycle Active' magazine has a 7 page spread on how to pimp your Tribble! Overkill is the one with the £250 upgraded wheel set and £330 pounds worth of leather saddle, bag, brakes etc. which kind of defeats the object of a £299.95 bike in my mind............but hey....all good clean fun!
I've tricked mine out with a few choice parts (Raceface Stem, saddle, Carradice Wedge-pack, new pedals, Swanky red 'specialised' bottle cage, new pedals, 'Tescos' cycle computer (don't knock it 'til you've tried it), pump and a few general bits and bobs but doubt I've even spent 3 figures customising it (yet!

).
The only major component I am a bit suspicious of is the very cheap tinplate chainset which I may investigate further.
Good Luck to all
w