I chose the 7x57 on your survey. I like the 6.5x55 also, owning several rifles in it. Just thought the 7x57, being an original chambering of the 93 Spanish would be better. Own several 7x57 rifles too, darn nice cartridge to shoot.
Someone suggested the 250 Savage, good suggestion, but if you reload, its brass is a seasonal run and sometimes hard to find. Nothing wrong with making it a 257 Roberts, a very suitable cartridge for the 93 Spanish action.