A good 1.60 gas engine will handle planes up to 10 kilo (22 lbs)
I am inclined to fly any plane, if the trust to weight ratio is 0.5. Ralph measured 17 lbs pull, and I a tad more on the MVVS, though frontal area plays a role here. At 17 lbs pull, I would fly a 32lbs plane. Performance would not be towering, but it flies.
To fly warbirds in a realistic manner, a sustained climb angle of 30 degrees is adequate. Once height is achieved (power equals height), that can be traded for speed (height equals speed). That is the way warbirds needed to fly to get an advantage.
I flew my high drag tow plane (16+ lbs) with a 26cc MVVS engine through an aerobatic pattern using the energy management described above. Nothing like an IMAC plane, but aerobatics just the same, and I would not like my warbird to have more power than that. (drag/weight ratio ~1 static, but less in flight).

Unless you want to fly 3D