My frame of reference is my .257 AI.Same bullets,same twist,I have backed off to only 3050 from my 22 in fwt bbl.with a 115 Ballistic tip.For the 20 years I have been shooting it,it puts a grin on my face.Sweet.Will whack deer and antelope fine.I have not used it on elk,I have larger rifles.I believe,if used with care and some restraint,it would work fine on elk.I might go Accubond or partition,and inside 200 yds or so.
Typical .257 bbls are not twisted tighter than 1 in 10,and typical .264 bbls are between 1 in 9 to 1 in 7.
That matters to the bullet mfgrs.You can get better deep penetration or extreme range and match bullets for a 6.5 mm bore.This may not mean quite so much if the .260 is limited by a 2.8 in mag box.Did you say you are converting an 06?I think your mag box and feeding would be easiest with the 30-06 family of cartridges,and,if you are a handloader,the 6.5-06 sure might solve the dilemna