looks like it causes some performance loss (up to 10 fps) on some gbc games. bionic commando, shantae, pokemon puzzle and wendy come to mind
maybe rs97 hw is not capable to handle this
Gambatte is more CPU hungry than Ohboy. On the GCWZero this is not a problem, but in the RS97 some GBC games (like Shantae) almost reach the CPU limit.
Also, there are some issues with the IPU hardware scaling and for some reason it's slower than software scaling, especially when doing non-integer scaling, like 1.5x, 1.66x, etc... However, this may be fixed in future retroFW updates.
Have you tried using software scalers or no scaling?