The seven-shot version would, in theory, be less prone to timing issues because the lighter cylinder (due to the extra hole) would have less inertia during fast DA shooting and thus less prone to wear the hand, ratchet, cylinder stop, and cylinder stop notches.
The difference in weight, howeverr, is fairly small (a 2 1/2" barrel 686 weighs 34.7oz while a 686+ with the same barrel length weighs 34.1oz per S&W's website) so it would likely take a copious amount of fast DA shooting to ever appreciate the difference.
Smith, and Wesson, and Me. -H. Callahan
Well waddaya know, one buwwet weft! -E. Fudd
All bad precedents begin as justifiable measures. -J. Caesar