VERY different beasts. Acros is also not quite panchromatic, or as panchromatic, or something. It has a different look, very worthwhile on its own but sure not Plus-X.
I like FP4+. I got into medium format after Plus-X was already gone, but I've shot a lot of it over the years in 35mm. I'd like to have used it in 120, but alas not. The prices on eBay for 120 Plus-X of reliable vintage always go to levels I'm not going to pay. FP4+ is a very nice film. Not the same, but I don't think a photo is going to succeed or fail based on whether it's on Plus-X or FP4+.