In length and height, my 10mm longslide 1911 is fairly comparable to the GP100 4" I used to own.
The longslide 1911, firing hot Norma 200gr, is more controllable for me than was my GP100 with 180gr BB HC.
A G20SF is comparable in volume to my 3" S&W 13. There is a reason I normally shoot light .357 158gr in the model 13. Heavier recoiling magnums are not much fun in it.
To achieve comfortable controllability with multiple rounds of 180gr BB, for me, requires a well fitted grip on a 6" GP100 or 686 type, or else a Model 27 or 28.
If I want to shoot a gun that size, and am worried about 4-legged, fanged things, I have a 6" 629 which beats both the .357 and the 10mm by quite a margin (typically loaded with 255gr Keith HC Buffalo Bore, for woodland use).