Standard Remington rifling is 6 lands and grooves with sharp, 90 degree corners between the lands and grooves. The 5R system is five lands and grooves with 45 degree shoulders. This is the rifling system that Remington uses on the M24 sniper rifles that they build for the US Army. The theory is that this design gives a better gas seal, more consistent velocity, longer barrel life, less friction and better accuracy. That's the theory. The truth, I believe, is that if you have a good standard 6 groove barrel and a good 5R barrel, you won't tell much difference between them all other things being equal. Having said that, though, the 700SS 5R Milspec has been very popular and I've heard people say that they shoot very well. My buddy has one and loves it.
All the 5R barrels will have a 1/11.25 ROT, so it should do pretty well with heavier bullets. If you're looking for a good target rifle, jump on it. I think you'll be happy.
Jason