Last season, I purchased the MB's along with Vokey wedges and got the standard size grip on the clubs, the Titleist Tour Velvet .580. On the butt end of each grip is the number .580. I'm not sure what that number means, but it's time to regrip my clubs. I was thinking about the new Golf Pride VDR grips, but the standard size is only offered in .600. I'm also considering going with the Golf Pride Tour Velvet standard size and they are offered in .580 and .600. If I went with the VDR, would I notice a difference with .600? What do these number mean?