I've read a lot about the 5r rifling and only two things that I've actually given credibility to. This is all speculation and I don't know if it actually amounts to anything tangible more than the time it takes to type it on an internet forum, but here goes.
The first thing about 5r rifling is that the angle of the groove cuts lends itself to easier cleaning, and possibly less buildup of fouling. The second thing is a theory that the bullets get distorted less because no land or groove is directly across from each other because there are 5 lands and grooves.
That being said, I don't know that it makes a big difference. I bought a Remington 5r and I'm glad I have it, but I can't say with certainty that I wouldn't be just as well off with a 700 PSS or a 700 SPS varmint. The 5r has a 24" barrel whereas the PSS and the SPS varmint have 26" barrels, and I think I prefer the shorter barrel so far. Also, I think the stock on the 5r is shorter than the PSS stock in the for end to look better proportioned to the shorter barrel. Also, the 5r is stainless with a pretty green speckled stock.