os 46- is very good engine . do your self a faver if you can go 4 stroke 70 or 72 . i have a bunch of 46 fx's & after going to 4 stroke . i won't go back . don't know about the sig something extra . sig is a good arf builder . so are most of the others too. the extra should be about for say a third plane . depending on skills. good luck wrc-flyer