The answer is, it kind of depends....are you talking flex, weight, totally different brands?? Realistically, you WILL be able to tell a weight difference, but not TOO much in the flex department from a feel standpoint. It's all about getting the flex, kick point, all that good stuff that produce great launch conditions. Also, if you have a driver that was made in the last year or 2, then you won't find much better technology by upgrading the entire thing, so the shaft only option may make sense. I'd say go to your local pro, and trust what they tell you about fitting. There will be more than 1 shaft out there that can get you good launch conditions, and you may decide one feels better than the next, so there you go - decision made!