Considering a R3 (61cm) but concerned about whether it would be a good fit. I'm 6'5" with a slightly longer than average torso. Sounds like the frame will stand up to any abuse from my 200lbs. Any tall guys riding the R3 who can comment?

Well, I don't own one but, when I mapped out the geometry it pointed me to the 61....and I am 6'2", 200 lbs. The stack and reach figures on the 61 are virtually identical my current bike (62 Calfee). I think you would fit on the 61 but, it is likely borderline small for you. Just an off the cuff opinion though, so take it with the usual grain of salt.

Try this site.
http://www.competitivecyclist.com/za/CCY?PAGE=FIT_CALCULATOR_INTRO

You will have to enter a bunch of measurements and they will eventually give you an idea of the tyoe of components you need.

i'm 6'4" and a 61cm fits well under me

Have you considered the RS??