Hammer forged barrels generally have a longer barrel life compared to cut rifle and button rifle but you give up a slight amout of precision potential (though I haven’t actually noticed this with Sako TRGs).
That said, if this is a rifle you plan on keeping I’d order a blank for it when you think you are a year out or so of needing to replace it. This is determined by your current/anticipated firing schedule and consumption rate per session/match, etc.
I’ve heard of 300 win mag TRG barrels lasting 3000+ rounds. 300 win mag should wear faster than 6.5 cm.
The TRGs are awesome rifles; your barrel should last for quite a while.