My nephew and his wife have a pair of CZs in 6.5 X 55.
Both rifles group under an inch @ 100 yards.
Reloader 22 powder and the 140 grain Sierra BTSP do very well.
As far as the .260 Remington goes, I think it's ok with bullets up
to 120 grains or so. If you lean towards 140 and 160 grain bullets
in this caliber, the 6.5 Swedish is a better choice.
This is because the longer bullets will not have to be seated
deeply into the case. A longer neck and throat in the Swedish chambering
favors those longer bullets.
With a decent 140 grain bullet, the Swedish Mauser should be
a good deer caliber out to about 250 yards.
120 grain bullets will stretch that distance some, as far as
a slighty better trajectory goes as I recall.