I have the 6.5x55, the 270, and the 270 wsm. I like them all for different reasons. The 6.5 is a light kicking deer gun. I have not particularly loved the results I have had but it has never failed to kill what I hit. I shot 2 does with it last fall, both 1 shot. It makes a sound I find funny... almost like it's a kids gun or something... more "ping" than "pow". It's a mauser 96 action and kimber barrel. Nice gun.
I use the 270 for most of my deer hunting. I killed 2 good bucks and doe with it last year. One buck was a neck shot and DRT, the other ran 50 yards or so. The doe ran down hill, in the snow, at dark, away from the truck, maybe 100 yards. Each was a heart/lung shot. It's a mauser 98 action, can't remember who did the work... beautiful fajen stock.
The 270 WSM is new and hasn't found much action yet...
I used to use a 30-06 for all my deer hunting, and frankly, I think I got faster kills with it. I think the .270 is better than the 6.5x55, and I wouldn't be surprised if the .270 WSM is the best of the bunch... we'll see...