Re: 5R and 5C style of rifling
I haven't noticed any substantial velocity gain with standard bore/groove dimensions. If you spec a slightly tighter bore/groove, you can achieve higher velocities. I had a 22" 308 Rock Creek for a long time that had a .2995/.3075 bore/groove (if I remember correctly) that would outrun Remington factory 26" tubes by 25 fps on the exact same factory loads or handloads.
Be warned however that we've tried the whole tight bore/groove thing with other cartridges and bullets designed primarily for hunting and never been able to achieve adequate accuracy. The tight bore/groove idea evolved from the Palma crowd due to the variability of different international match ammo. It works great with match bullets due to their thinner jackets that obturate more easily. But add magnum speed and hunting bullets and things just don't seem to work very well.
As for cleaning, they do clean up a bit better. But I'm not a huge proponent of cleaning too much. Most barrels perform better (accuracy wise) after a few rounds. We generally recommend that our hunting clients sight in with the load they intend to use during hunting season, then clean really well, then foul with 3 to 5 rounds, go hunting and clean at the end of the season. Unless of course the barrel interior is subjected to some unusually dirty or wet conditions. We've actually noticed more cleaning differences between button vs cut barrels than between 5R vs standard groove barrels.