I did extensive prop testing about 15 years ago ( flying two cycle glo for 23 years )
The APC props out performed every other prop i used
My test for performance is the unlimited vertical ( straight up from level flight at full throttle ) and APC props would pull me higher and faster than any other

The 12/6 should be good on the 61 SF
Is what i use on my 61SF
It is a long stroke engine unlike many earlier 60 size engines and will not like the 11/7 ( that is a higher RPM prop)
The long stroke is a torquier engine and one of my favorite engines for power output in its size

Do realize you always prop the airframe for-- its best possible performance with a given engine

Always balance every prop you use

All prop are dangerous but APC is a meet slicer - so Beware !
Do not get distracted and focus when working around a running prop

Use a chicken stik or electric starter to prevent being cut

The largest prop you can use with the lowest pitch you can use --to run the engine at the Mfg recommended RPM ( on the ground ) will always give you the most control feel flying where you will need it the most
Best power output for manuvers and throttle control on final

Above applies mostly to two cycle glo as that is my thing
The engines from 46 to 1.08 glo would be best for APC but the engines larger than this - wood props are just easier to use and aquire
Expense in the larger size props is an issue to consider always

Enjoy