No, it makes no difference, using synthetic does not effect ring seal either. 100% MYTH. Dyno sheets showing an appreciable difference in hp between motors due to oil use is first off impossible. You can setup tests showing long term effects of oil, but to say using dino initially gives more hp or better seats the rings is myth. You will not find one article, or repeatable procedure, that shows any kind of proof at all whatsoever. Too many factors involved to get a proper test. There could be atmospheric differences, there could be differences in the quality between builds, there could huge differences in the seasoning(ie final shape of the cylinder bores and other tolerances throughout the engine from breakin) of the motors in question.

So Ill say it again, you can run synthetic from day 1, and I recommend it. There is not one single reason why not to. But I can give one good proven reason why you should. Initial startup of engine does benefit from synthetic. Since the engine is starved for oil for the first few seconds, running synthetic oil in combination with assembly lube assures that the engine during this critical phase is fully protected and lubricated upon initial start. Critical areas upon start will heat up superquick(piston rings are very sensitive to excessive heat and can be damamged within seconds) due to lack of oil and synthetic oil is better able to withstand quick thermal breakdown due to friction and combustion.