Interesting, have you ordered a factory rifle and therefore a standard dimensioned chamber or a 'custom' job ? Factory ammuntion is available I think, but very limited in bullet type and weights. The 260 is really a reloaders calibre in UK if you want to get the best from it , thats MHO at least.
The thread that BB refers to involved my self and the semi custom Tikka 595 shown there.
Martyn is one of the better sources of info on the round, and he certainly puts more thru his collection than I do, so you might ask him for load info.
Martyn and I got into a discussion that revolved around Vit N140/150/ 160.... concensus was that N150 and N160 are probably the way to go with our short throated barrels and using 100Gn Nosler BTs... which are very adequate for all UK deer, in our experience anyway.
I have just tried H414, with excellent results and the same Bullet tip....
I am going to try some 120 Nosler BTs ...... loaded them but not tested them so far, as I am away working until end of the month .