A 1 in 8-inch twist rate is fine for most 140gn 6.5s. There are two issues with the 6.5X47L and 136-142gn bullets. Unless you ask the rifle builder to throat the chamber for these bullets, they normally arrive with enough freebore for 120-130gn bullets, but insufficient for the longer models. That gives COALS around 2.650-2.700". If the rifle is set up the 'heavies', COALs with the bullet just off the lands are in the 2.795-2.810" range.
With longer FB set-ups, some people have had very good range results with the cartridge and 140s used in long-range competition, but others have failed to make them work no matter what they try. The size of the cartridge / case capacity seems to see it ideally suited to 123-130gn bullets and so heavier models become a bit of a lottery. I know one or two people with rifles in the calibre who started out insisting on 140s, but went for the shorter FB and shoot the 120gn Scenar L or 123gn Scenar now after rebarrelling.
The Creedmoor chamber was designed by Dave Kiff at PT&G and Hornady's Chief Engineer Dave Emery around the 140gn AMAX at exactly 2.800" COAL and this weight / length of bullet is optimal for the cartridge. It will perform very well with some lighter bullets too, but unlike the 6.5X47L, I regard the 130-143gn bullets as the default choice for this cartridge.