For a comparison that has a lot of examples all one needs to do is look at the old FAI F3A engines. These engines were held to a 10cc displacement for the two cycle and 20 cc for the four cycle. Now all one has to do is look at the record book to see that even with 200% advantage the four cycle engine was hard pressed to beat the 2 cycle for a myriad of reasons. So for aircraft that were/are critically judged the two cycle is the superior set up for our toys unless one give the four cycle an inordinate displacement advantage. Now in this example both engine types were competition engine. For the sport pilot the formula might not be the same.

All the best,

Konrad