As long as you are comfortable flying the 102" Yak go for it. It will take you much further than Sportsman. I would say you would be competetive through advanced with that plane. If you want to be competetive in unlimited you will want every advantage you can get so a 40%er might be the way to go but the 102 Yak will be capable of the unlimited sequence.

One thing you will find is that the more time you spend with the same plane the better you will fly. Starting with a 50cc plane and then moving up to a 102 incher isn't bad but my suggestion is to get one plane and fly it a lot.

Dan