Re: Question for you Remington Pro's.......
I also believe that with theSenderos, you are paying for QA/QC, the same way the barrel manufacturers grade their barrels according to QC tolerances.
It's not that an SPS isn't capable of performing as well, it's just that they aren't offering accuracy guarantees at the SPS price point whereas you almost never hear of a Sendero that doesn't shoot extremely well. If you get a good 'smith to take a look at things, they start to have control over QC and can rectify things not taken care of at the factory.
I believe anyone thinking about going the semi custom route is well advised to go the SPS route. For the cost of Sendero, you can probably get a stock fitted to your dimensions, proper bedding, trigger job and the action blueprinted. Plus, you have the benefit of getting work performed over time, so the hit to the pocketbook doesn't sting as bad.
As others have mentioned, heavier barrels often provide better accuracy than small barrels, especially in longer barrel lengths. BR guns don't wear them for no reason! Again, not that you can't get great accuracy out of a thinner barrel.