In terms of longevity of the motor, oil won't make a difference at all. In terms of shifting, I have heard people go from synthetic to regular and state it is so much better, and of course the opposite way. Here is part of a post I just put up on Facebook earlier today. This is from the wife's 109.
I already decided to do a full rebuild so we tore the motor down. 81k miles on this motor and what did I find? I found that I was amazed. The crank and rod bearings are in great shape. Obviously they have wear, but no indication they wouldn’t last for many more miles. The transmission also, no issues before tearing down and is in great shape. The shift fork has a mark on it, but no grooving at all. She complained that every now and then she had a grinding from first to second, but I truly believe that was her on a lazy shift. In the lower case, there was not as much as a spec of metal and not even any flakes. If you put this motor next to a 5k mile motor that was tore down, I think it would be hard to tell the difference unless you knew which was which.
The end result is that she has all new bearings, oil pump, crank balance shaft bearing and a back cut transmission and rings going in. Cylinders were hones as well. Sometime this week I am hopeful to pick up all the parts and start putting the motor back together.
This isn’t another oil post, but some have hit me up to ask what we are using. Since the very first oil change, this bike has only seen Valvoline 10wx40 NON-SYNTHETIC oil. It is in a blue or black bottle. It is called v-twin or 4stroke oil. I have changed her oil every 4k miles, or slightly under, and always used a HF138 Hi-Flow oil filter.