I really dont think there can be a comparison between off the shelf and full custom.
Ive owned a lot of rifles over the years and shot just about every brand.
Factory will do the job, but dont expect to own something that someone else owns a few miles away - i.e, youre not buying exclusivity.
Factory performance - well, some group, some don't, you may be lucky and get something that groups circa 1/2", you may not and buy something that groups 2", no matter the brand, you never know untill the time you spend on the range and by that time, its too late - its performing "to factory standards"
A recent thread about a well respected rifle brand highlighted the fact that several people couldnt get "brand A" rifle to shoot consistently - yet when it was tested independently (by me), it shot quite well for a factory gun..
Again the point im trying to cenvey is that the factory gun may not suit you and you wont know this untill you squeeze the trigger the first few times.
Full Custom - you can pay bettween 2k to 10k or above depending on where you go.
A full build using a custom action, barrel and stock will perform (or should perform) far far better and more consistently than factory guns.
Again, you pay your money and take your choice with whoever you choose to commission the build on, but all the way through the build process there whould be a dialogiue bettween you and the builder so you know what stage theyre at and exactly what you're getting at the end.
Its been muted that theres no difference bettween the accuracy of factory over full custom - frankly I think this is bunkum.
I shoot numerous competitions per year at shoots for sporting rifles (and compete elsewhere) so I come across loads of guys with both factory and custom guns.
Every time id say the customs group far more consistently than the factory entrants (providing the user is on the ball)
At the end of the day its your money and your choice, I know which way id be going and have built and used enough custom rifles to know the smart choice is a full custom build, using a proven, quality action and barrel, with a stock of your choice, this will provide you with the confidence and pride in ownership for many many years to come.