A .60 in an 8 foot telemaster equates to (12/8)^2*.6 =1.35. Actually the compareson should be the weight or displacement of the two planes but this should be close. If you know the finished weight of both then take the larger planes weight divided by the smaller and mulitply that by .6 to find an equivilent size for the larger plane.

Using Hobby Lobby's weight then 23 lbs/10.5 lbs *.6 = 1.31 So the 1.6 should give the 12 foot plane better performance than the .60 on the eight foot plane.