Back when I built my 6.4-'06 c.1982 the available barrels were 1 turn in 9" twist, so that is the twist of the Shilen barrel I used. I have shot different bullets in it besides the 140 gr Spire Points I normally used for hunting, but only the Barnes Original 165 gr Semi-Spitzer showed stability problems with groups opening to 4+".
The data I have from that period showed a 7.87" or 200 mm twist as common for 6.5mm rifles in Europe.
jim
