My sheet wing Skyfire was about the size he is considering at 230 sq. in., but it had a spruce spar and a tapered wing. Even so, there was some flutter problem and eventually I cut the span down 4”.
Also, it was 061 power. I had a Skyray with a Black Widow, and it was just fine as is. If it was to be enlarged, it would have to some how be made much lighter.
If I were to mess with it, perhaps a 5% upsize, go for a 1/16” thick wing with a spruce spar and carbon veil covering, a hollowed, laminated fuselage, and lightening holes in the tail surfaces. Nose moment adjusted to eliminate need for ballast, of course.
Or, on second thought, why bother. Buy a Cox Medallion and build an PINTO from an RSM kit and have a really superb model.
Or, I modestly offer, an 061 and my own RSM kit SkySport.
Either of these will do a 500 point pattern in the right hands (not mine, sadly to say).