The 6.5-06 AI was and is still a lot of fun to shoot and can achieve good performance. With that said, I will not build another after my last barrel is toast.
Depending on my desired speeds, I will do a 6.5 CM, 6.5 PRC, or 6.5 SAUM. I will most likely stick with 6.5 CM.
I would build a 6 CM for 6 mm. I see no reason to shoot a 6 mm faster than the 6 CM is capable of. I know
@Ryan Avery likes his 6UM, but I don't think it's worth the trouble or lack of barrel life. My experience says I will hit as many targets and kill just as many animals with the 6 CM versus the 6UM.