The real parameter you should be considering is the wing area. If you have 600 sq. inches of wing area, your airplane will most likely fly well. I don't do 4 strokes as I never really understood why a person would want a heaver engine that puts out less power than a 2 stroke that for the same displacement is at least 30% mor power, easier to operate. I did use one and OS 120 for a couple years. Far too timid and touchy for me. I have a couple now NIB, Saito 150 GH and a YS 1.40 something or other also NIB. had 'em fo 5 years or so.

Back to your question, generally the 4-stroker is heavier turns a bit more prop at less RPM and is more tempermental. However if such is your choice, and you have a 6# airplane that has 400 sq. inches, of wing and you ask that question, you won't have to worry about it very long. It will be gone to the Happy Flying Ground. On the other hand, if your model has 800 sq. inches at 6# you might have considerable fun with such a plane as long as you are not trying 3D.

As an example in this picture taken 6-7 years ago that big red high-winge with much dihedral is a replica of the GUFF, Dr. Walt Good's original RC airplane first to be flown in the USA. It operates on 3 channel (Dr Good only had a rudder that was L or R or Center. ) A Como (Sup. Tigre) 60 hauls it off the ground in 15 ft. I do loops and rolls A-OK. Cruises well at half throttle. Thermals well. I think - without going out and measuring the chord - the wing is 1200 sq. inches +/- with a 96" span and it weighs 9#.

Hope this gives you some background info. for modeling performance.