There are variations in structure within the ".60 size" class that make it impractical to say for sure. A kit can be labeled .40 to .60... and people will call it .0 size. it could also be labeled for JUST for a .61 (that would be a larger mnodel than the one labeled .40 to .60...) and REALLY be a .60 class model.

Generally its OK to exceed the listed engine size by one upgrade. (if it saays up to .61... .72 is not too far out of line)

When replaceing a 2-stroke with a 4- stroke, a .52 4-stroke is about the same power as a .46 2-stroke. .72 replaces .61, .91 replaces .72. 1.2 replaces .91. (it'd be closer to use 1.05 to replace the .91... but find one...)

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BTW... sticking too large of an engine on trying to gain performance... you don't always get what you are after. Larger engines generally weigh more. Low speed performance can suffer severely. And then... putting a .91 4-stroke on a Four-Star 40 (as i have seen suggested once) its not the weight that wll be a problem... you can litterally pull the airplane apart with the excess power.