I have an SR25 and I love it. The can they make for it, the QDC, it's really nice. It's more than the one you have in the link there though. I agree with looking at the other brands for the price, lots of people love the LWRC Reaper, only hear good about 'em. I don't know much about the others only to say the first DPMS LRR's back in 2003 sucked ass, period, so I do know what a shitty one feels like.
I'm not a piston guy but I'm guessing you're thinking about gas in the face, yeah? The PRI charging handles work pretty well. The KAC rifle isn't that bad anyway, it's not as bad as the small frames for sure. But a short stroke piston is cleaner. I guess were I to get one with a piston, I'd get an SCAR though, maybe one of the new precision ones, people are saying they print tight groups --that'd be a nice investment and surely fit the bill.
DI isn't necessary on the large frame. It never was designed with one. The FA is a 5.56 item since the BCG doesn't have as much mass as the 7.62. It'll always lock up fine since the BCG is massive on those. I know what you mean though, I was a big FA guy too until I read the facts on the SR25, which Stoner himself designed. And when you think about it, it's all in your head really, no other rifle like that has one, not the FAL or H
JP Ent. is another mfg. of very nice rifles. HK's are nice but I don't think their products are worth what they charge, more than an SR25. Larue supposedly makes a nice one, didn't wanna wait a year on one back during one of the Obama rushes. GAP was one I considered but they wouldn't do one small customization even if I sent the parts; turns out GAP ended up having problems. Not sure about SIG 7.62 AR's, I've heard some people complain. LMT makes a really nice one and now Noveske finally makes one after all this time, the N6. They make a really solid AR so I bet this one is probably pretty nice too. Most all these are DI too, some have a FA but most don't.