Re: Optimum Bullet weight for 1:10 twist
"Is there any truth to what they have told me? "
To put it politely, Doo-Doo. In terms of pure benchrest accuracy, yes, you don't want to spin a bullet faster than necessary to achive about a 1.2-1.3 stability factor. For real world shooting, it's not an issue at all, unless you're using really bad bullets. Basically, spinning a bullet faster than needed accentuates problems in jacket wall concentricty. If the jackets are good, there's very little error to be magnified by the excess spin. If you're building a target rifle, and have the luxury of knowing preciesly what bullet you'll be using (often to the exclusion of all others, as in a Palma rifle) you can match up the twist rate very well. For most hunting applications, go with something that gives you some latitude in bullet selection.
The 1x10" was originally intended in the 30 cal to work with 220 grain bullets, and has been handed down ever since, as much by tradition as any real ballistic requirement. It's still handle some pretty heavy bullets, but will also do a pretty good job with the light weights as well, assuming they're good quality bullets to begin with. I'm willing to bet you that with a bit of work and a little load development, you'll be able to get the 165-168 grain bullets (as well as some lighter ones, too) to shoot just fine. Enjoy.