What bullet do you want to shoot? Your question is too general. I run a 1:11" twist in my 300 WM and shoot up to the Hornady 225 grain BTHP bullets. If you want to run the Berger 230 or 240 SMK, then a 1:10" is needed. I prefer a 1:11".
^^What Chad said^^
If I'm building a 300 Win Mag or 7 Rem Mag they will have a 26" barrel. Ya got all that powder, ya need to give it room to burn, and still be inside the barrel.