I dont think you'd be harming anything by the switch. You may end up losing a mpg or two but thats all I can think of, there may be more...
What made you decide to switch out from Syn? What do you plan on switching to? I would think with your millage the Val max life would be a good candidate.
Im on the opposite side of the spectrum, I just switched to syn at 186,000 when I bought my SVT as I figure it will help clear some of the build up from the high millage, and I dont need to change the oil as often.
