Rich,
I've had both, 1st a sport tour and now a tour. I think I recall Andy B saying that there's about 8 oz difference in the frame weights.
I found the tyre size restriction of the RST the limiting factor for me. It's ok if you only want to use 1.5" Hi-Roads, or 1.75" Tourguards, but I found the availability of other tyres limited.
I did not find the RST particularly sporty, compared to my other 700C bikes and I don't find the RT much different than the RST in this respect.
Im currently running 2.0 Marathon supremes with a 38:16 ratio. Unless your riding it as fast as you can I find this fine and can ride at 20 mph with it, how much faster will you/can you go? I'd sooner run out out gears going downhill, than going up.
I'm on a 586s (I'm 6'2") and find that with 1.5" tyres the wheels look out of proportion to the frame size, though obviously this is just down to looks, but who wouldn't want to be happy with the look. 2" tyres looks far more in proportion in my eyes.
Good luck and enjoy!
Steve