I've been a long time Larue customer, but until recently it has been all mounts and normal AR15 rails. Edit... and how could I forget, lots of triggers.
Like others, I jumped on the recent lower sale, so now I'm looking at some of their complete rifle and upper specs hard for the first time, and wondering what specs differentiate various products.

Initial example:  I'm comparing the 6.5c Match Grade upper (current MSRP $2k) to the 22" PredatOBR complete 6.5c rifle (current MSRP $4300)
Based on the specs on the Larue website, the only differences I can see are:

On the OBR rifle:  QD rail and 1:7.5 barrel
MGU:  Rail bolted to the upper and 1:8 barrel

Even if you go crazy and assign $1k value to the lower, you'd still seem to be at a four figure value difference between the OBR upper and the Match Grade upper.
What is accounting for this?  Is the barrel on the OBR different in ways other than the twist?  Are there any other differences I'm missing?
Thanks for any input.

As far as actual difference there us not much between the uppers.  Complete rifle may have the Port Selector Technology (PST) gas block, essentially a two setting adjustable gas block for suppressed and non-suppressed.  Like you said the uppers and handguards are different, and the quick detach is only on the PredatOBR rifles.

The major drivers in cost difference (hard to equate when you price out parts) is the parts and assembly of the lower, the accessories included with the rifle, and the 11%(?) Federal Exercise Tax on firearms.  The tax was the driver behind the Ultimate Upper kits years ago.

Tobrs are test fired and come with the test targets.

Thanks... no major differences in the barrels then?
I think I'd rather have the non-QD rail anyway.
Two position gas block sounds like it could possibly be nice, although I don't see that mentioned in the description nor listed as a separate item on the website.
Looks like the complete rifle comes with a couple mags.

In any event, 6.5c MGU is headed my way.

The mags alone are/were around $100 a pair, probably more now with the increased pricing. If you’d like an adjustable GB SLR makes one for LaRue pattern barrel dimples. The idea behind the QD handguard was for quick change calibers via barrel cartridges or to break the entire rifle down into a smaller package. Realistically, if you want to swap barrels it’s only 4 screws and the barrel nut.

Wow, you're not kidding, $182 a pair now.
I guess that is some of it.

Hopefully PMAGs work... I notice they don't drop free, but this isn't exactly going to be intended as a fast handling carbine anyway, so probably not so much a big deal.

Good info on the SLR gas block, I will keep that in mind.

Pmags will work and in time they’ll drop free just fine. LaRue rifles have very tight tolerances. I forget off the top of my head which particular SLR you’d need for the correct spacing. I want to say the 7, but I’m sure someone will have the correct one if I’m wrong.

.450 spacing on the gas block IIRC. I think it's the Sentry 7. I've never put one on an AR10 so I'm not 100% sure.

Does anyone know what barrel coating/treatment is used?
And would it vary by upper (OBR vs "ultimate upper", vs "Match grade upper"?)

The upper just hit my doorstep.  Everything looks beautiful so far except the gas block is just slightly clocked... I find that pretty common with most brands.  I wonder if the barrel is already dimpled... if not I could probably straighten it without impacting the gas flow.

They are dimpled and the screws are secured tightly. You need heat to remove them. The two outside screws and then the middle IIRC.

If it's already dimpled, it pretty much is what it is I think?
I'm sure it will run fine.

I suppose it’s possible that they slightly missed the dimple on assembly. Only way to tell short of removing it would be to check if the screw is flush with the bottom of the GB.

So besides the gas block cant, there were also some dark splotches in the chamber that I couldn't get to clean off with Hoppes patches, and I couldn't identify (leftover cutting oil stains or something?  I'm not a machinist).
It probably would have run fine, but I knew it would always bother me, so I sent it back.  The new (or fixed? Not sure) one hit my doorstep yesterday.  Everything is beautiful.

Took it to the range today, and got all of 12 rounds through it before it started pouring rain.  Unfortunately between having an old school chrono, and very little 6.5c ammo (and at over $2/pop for factory) I shut it down since I need all the data I can get from each round.  For the Larue, the day consisted of:

2 rounds at 50yd to get near zero.

5 rounds of factory Hornady 140gr ELDX at 100yd.  Average 2621fps with the best ES and SD I've ever recorded from a firearm that I own; obviously a small sample size, but still.  Group size 7/8ths".

5 of my lightest ladder test load that I put together this week, 38gr H4350, 140gr Midway seconds (likely SMKs) at 100yd.  Velocity average 2425, group size 1".

Surprised that the gun ran and ejected both those loads to the exact same spot; I don't think any AR15 I've ever shot would do that with velocities that far apart.
So not a single bad thing to say today based on a very small sample size.  Definitely looking forward to shooting it some more.  Also I really need one of those new Garmin chronos.