I find Sash & Sabre fits right in with Perry's Metals and Plastics to the point most people would be hard placed to pick out the difference at any distance.
Personally, I also use Steve Barber and Foundry. These are both a bit bigger, but not to the extent that it bothers me.
In this photo you've got a Perry metal command group (officer, flag bearer, drummer). Now all of the other figures on the front row are Sash and Sabre. The back row is all Perry's plastic, with one exception. The guy in the brown floppy hat, reloading, is a Steve Barber figure. To me they all look fine together.