There's a patch on the wiki (link below) that really improves the FPS for me:-
https://wiki.rpcs3.net/index.php?title=H...Killzone_3
With some carefully chosen settings I can get 15-30fps in the first few missions after SPU/shader compilation. I would say it actually runs slightly better for me than Killzone 2 on my specs (i5 6600k oc'd to 4.5ghz, GTX 970. 16gb RAM).
Unfortunately the loading times are crazy, at boot it just sits hitting the disk for ten straight minutes before displaying anything and sometimes in-game too. This heavy disk mashing seems to cause a crash at the beginning of the "Broken Highway" mission and I can't get any further into the game.
EDIT: I might have found the source of the crashes - for some reason, setting SPU Loop Detection to ON improves the stability a lot, but the performance is worse and the sound stutters badly in heavy scenes.