Hi,
Hope you are well. Quickly saw this post and remembered me of this quick PG I did:
Might be of use to you?
Else, as per using or not using a physX engine and for what purpose, this is very much depending on your scope. Of how much importance, precise collisions are essential to your project (for collisions) but I suppose moreover, whether you have other features that require physics (like i.e. shooting, object with a mass, objects that require to transform or move with an imposter, etc…). As shown in the PG, you do not necessarly need havok to move and collide a character along the map. The rest, as I said, is really depending on your scope and expectations. I hope this will help you make a decision and meanwhile, have a great day 