The more time I spend in the company of rifle shooters in the UK the more I believe that custom rifles are more for show.
Most hunters in the UK will shoot up to 300yds max, occasionally you may get a few that will stretch the legs of the caliber and get out a bit further, but not many.
I have a Tikka T3 super Varmint that gives me .5" groups all day at 200yds and 1" at 300yds. With that kind of accuracy why would I want to pay anything up to £5k for a custom .243 rifle???
Yes it will look better for certain,
Yes it may give a very slightly better group,(But not guaranteed)
Yes you will have a rifle to your exact specifications.
But will it shoot better, Maybe.
I have a friend that paid £6k for a custom .243ai and we go out hunting together regularly. His rifle is an absolute beautiful piece of craftsmanship, but I can outshoot him with my factory .243win every day of the week.
I have tried to shoot his rifle and yes it gives 0.5-0.7" groups at 100yds for 5 shots, but my groups are way better.
He has tried changing powders, bullets, seating and primers and it just will not shoot better.
Unless your shooting at extreme long in range in competitions custom rifles are really not an absolute essential, they are nice to have, but not essential.
Check this guy out on Youtube with his factory rifle.
In addition, Remington, Sako, Blaser, Sauer,Tikka may know something about accuracy too !!!