I guess the first question is: what is your purpose of the build? Competition (what kind)? Hunting? LR plinking? What about your budget/preferences? These will dictate your choices and help others in helping you.
Here's a pic of the rifle in question (been posted here before

) .
Remington SPS-V .243
I don't participate in any competitons as of yet. Not a hunting rifle either. LR varmint/plinking/bench/tacticool rifle, Call it what you want. I just
love shooting this rifle and want better accuracy from it, the next logical step is a match barrel & some work done to the action to achieve this. There are very few places to shoot LR in Quebec, so your looking at shooting under hydro lines in the summer and across secluded frozen lakes in the winter. I would love to eventually find an area where 1000y shooting fun can be had safely in my area.
I was planning on going with a heavier 17A contour krieger so felt recoil shouldn't be a problem up to and including .308win. I aware of how recoil can and will affect your shooting, but funny thing is, lack of recoil is a little bit of a turn off for me

I've owned target rifles in .223, and still own a .22lr bench rifle and they all lose their appeal after a while, as accurate as they are, I always end up feeling like I'm shooting an air rifle. That is why I ruled out the .223, and I'm having doubts that a 6mmbr in a heavy rifle such as this might have the same outcome. Silly priorities I guess.
The extra cost per round and lack of quality brass available for the 260 bothers me. I want something practical, and Im not planning on spending the extra time to prep .243 or .308 lapua for the 260. I'd have to settle with sorted r-p brass.
As for accuracry, are both the 6mmbr & 260rem similar to 500y?