How many out of town guests can i expect to make the trip?

Always prepare for 100% attendance. People always travel to weddings with zero issues regardless of distance.

Personally, for my (local) wedding, I am expecting a ‘no’ rate of 10-20% of guests. The fact that your guests have quite some distance to travel, I would safely assume at least 20-30% of RSVPs to be ‘no’ BUT this depends very much on your crowd and you know them better than I do. With that said, as PP noted, be prepared for the possibility of 100% attendance (although I personally have never known anyone’s wedding to draw the full crowd).

Prepare for 100% attendance until you get final rsvps back.

Ours is a similar 4-5hr driving distance for many guests, but a flight for a some. Many estimates say 80% for a driving destination.
Honestly, I did an expected value calculation (sum the probability of each guest attending) to get a better guess. We have some family that almost certainly won’t make it (financially not feasible) but other friends who have verbally committed that they will definitely be there. My detailed estimate puts us around 70%. I also estimated a minimum attendance from this (for food/bev minimums etc).
We are mentally planning for around number, but we can accommodate (space and financially) if do get a much higher acceptance rate. 100% is pretty unlikely, but a close friend had a destination wedding in Mexico and she had over 90% acceptance and it was almost a problem fitting everyone!