I have a U CAN DO .60 with a four Stroke OS .91. If it is hovering well then it obviously has the power you want. Why do you want to change??? I think from the 50 bozillion posts I have read that the Saito 100 or YS 100 class are the ultimate engines. On the 46 size I think the OS .70 FS or a YS Saito four stroke of similar size would be a great choice, I have seen them fly well with that size engine. But, run the most powerful with the least weight and most dependable engine you can afford. I love the OS because in my experience they start easily, run reliably and have great power. I have on deadsticked once on my new OS .91 surpass w/o pump and it was my fault it happened.