I’ve got a P7 from a few years back (2004 maybe) where the recommended maximum was 130. I had 140 Pikes on and felt the difference but it didn’t ruin the bike. I can’t describe the difference but it just felt a little bit wrong.
You’ll probably be fine with either 100 or 120 but given the choice I’d pick 120.
I’d imagine a frame designed around a 140mm fork is going to be a bit twitchy with 100mm of travel. I had a 130mm Soul a few years ago, & that certainly was at 100mm. 120mm would probably make for a good compromise if you want something a bit more xc biased.