I can give you some really good advice that comes from having a 6BR, 6BRX and .20BR ......all repeaters
A 6BR would be an awesome choice, but it really boils down to if you want a repeater or not. You can get the 6BR to feed fairly reliable, but you will still have some issues now and then.....especially if you get into tactical type matches or just fun matches where you may want/need to cycle rounds quickly....which by the way....you can do with single shots as well with practice.
I am currently gathering parts for a 6SLR build. So, although I haven't even been around an SLR, I'm a litte biased. YOU SHOULD GO WITH THE SLR