I find plus-x and fp4 very different in character. I like plus-x very much in 120 in Rodinal. Indeed, in contrasty light-conditions I find it perfect. A bit less dramatic as Tri-x but very correct. In D76 though I find it dull. In 35 mm I prefer fp4, it seems in 35 mm really sharper than plus-x. So just as others said: try both and taste.