Leave it as is, i shoot the 150gr berger VLD out of my 270 Tikka at 2900fps. At lower elevations i can kill deer out to 650 yards nd high elevations out to 800 odd yards. Longest kill with it was 810 yards, sacked on the spot.
I regularly use it between 300 and 600 yards on stuff
you can actually just drop to a 130gr projectile to reducer recoil and still have heaps out to 600 yards or so.
If you really want to change to a short case then just go 6.5 Creedmoor, i have owned both and realistically the 270 outshoots the 6.5CM with a decent 150gr load on trajectory as well as retained energy down range and maximum kill distance, but the tradeoff is more powder and more recoil.
You wont gain anything by going 7mm08 as a decent load in that recoils about same as 270 especially if you end up shooting 150gr plus bullets, i used to have a 7mmo8 as well.
TO be fair for NZ game, even if you go 6mm Creedmoor and you load it with a 100gr plus bullet with a good BC you will still be sweet for reds out to 500-600 yards but as you go down in caliber your shot placement becomes more critical.
I would keep it 270, maybe suppress it and load 130s if you are looking at staying under 600 yards. Load the 130 gr SST for the main load that you zero it on and use for long shots, then load the 130 interlock as a closer range bullet on the same load and zero.
Rebarrel job is gonna cost you over $1000 if buying a new barrel, that is a lot of ammo money spent on very little gain.
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