The new XCRs are smoother operating, lighter and more slim with the Keymod rail. The Type 3 gas system has more adjustability. They are basically just more refined than they were and RA has upgraded a lot of parts (not sure if you've upgraded your older ones).
The downside is the new Type 2 bolt won't interchange with your Type 1 lowers/bolts....so you can't swap straight across unless you convert the lowers and buy the new bolt/carrier/firing pin/buffer assemblies for your old ones. Personally, I don't think the Type 2s are really any better than the Type 1...we've seen at least one broken firing pin with the Type 2 here, so that obviously didn't fix that relatively unlikely issue.
Does 300 BLK have an equivalent to the 40 grain V-max from Hornady for .223? I'd think that a supersonic round like .300 for home defense would have similar overpenetration issues to 7.62x39 unless it's got a very specialized bullet design/weight like the V-Max....though you may be thinking subs.
I'm biased AF.....I love my XCRs...so I'm not impartial on the Virtus. I'm familiar with them, I just don't really care for the bolt design, ergos, limited calibers or brace options comparatively....I think the XCR is way better built, once you get it running. That last part said.....
RA's quality is much improved, but...I've bought 9 of them and only 3 so far have worked out of the box. To be accurate though...the ones that did run 100%, were all 16" bbl models (2 Ls, 1 M). But my most recent purchases of even the newer designs have had gas issues and didn't work until I modded them....one was a 12" M in .308 and the other is a 11" L in Grendel (still working on the 6.5G). In sum, none of them had major issues....they needed relatively minor tweaks to get running 100% reliably without cleaning or lube on absolutely shit ammo, so to me, they are worth the extra hassle.
SIG USA's quality isn't the best either....look at the P320 drop safety debacle or the first gen SIG 556R and their often contradictory advice from service reps when you call/email. It happens in all companies. Sig isn't a boutique company though...they are mainstream and likely to weather any economic downturn.
Side note: if you want to bury your can inside the handguard, go with the Sig. Can't do it with the XCR.
All that said, b/c there's no shit steel case ammo for .300 BLK, I'm betting the XCR will run out of the box.
Mick and Nate both own MCXs....they are probably your best bet for a fair comparison. Hopefully they'll chime in.