How big of a difference is there between a regular treeless and a wide treeless? I've heard that they fit pretty similarly once they're broken in; is this true??

I'm out of it. I had no idea there was a wide treeless. I ride in a Bob Marshall treeless. 

Same I ride Bobs too....didnt know there was a "wide".

Circle Y's Tammy F and Jackie J had the option to buy regular or wide.  I had a wide and it tended to roll on quite a few horses.  I bought another that is not the wide tree and it fits almost anything I put it on that also fits in a 6 3/4" gullet regular tree saddle.  It was too snug on my gelding that had to have a 7 1/4" gullet. Hope that helps.

I think I remember reading years ago that the BM had a barrel saddle and a trail saddle pommel and cantle style available and that the trail one was a wider pommel version which kind of makes sense as my neighbor man had bought a trail version, ended up hating it and years later just gave it to me. I do a lot of my weekend riding when I 'm riding all the horses in it so I don't have to climb in and out of the tack room to get the other saddle that fits so and so better, I just change pads according to whom I riding instead. Never had any issues with it, then about 4 years ago I bought the TF wide fit barrel saddle for my older gelding. Again fits all 4 of my horses.  My BM trail saddle is pretty hard used since I've had it for 18+ years, so 3 years ago I had an opportunity to buy a BM barrel saddle and loved it...untill I went to make my first run in it!  My then 10 gelding bucked like crazy at each and every barrel!   Never had done that ever.  Next event, same thing. So went to the trailer and put the BM trail saddle on him because that is what I had, the TF was on the old gelding whom I bought it for, and no more bucking in the turns.  

I've talked to Tammy Fischer herself about this and she said her regular treeless saddle over time will end up being a wide. 

So that must mean the pommel width are the same on both?  That is interesting to me and almost negates it being a "wide"....

What brand of Treeless are you talking about,

Theres the Bob Marshall and the Circle Y's that make the Jackie Jatzlau and the Tammy Fischer, now I know you can the Circles Y's in a wide but not to sure on BM since its been a long time since I have ordered a BM.

The Circle Y Tammy's and Jackie's have wide and regular. BM has a trail pommel which is wider than the barrel pommel but they don't necessarily have a "regular" and "wide". 

So I'm not crazy that the Trail saddle for the BM is wider pommel!  I thought I remembered years ago someone who was pretty knowledgable stating that but I didn't ride treeless saddles at the time. All I know is that my 13 year old gelding was fine with me making a run in the BM trail saddle but bucked pretty good going into and around the turns in the BM barrel saddle I ended up getting because the trail saddle was just way to big a seat for me, felt like I was getting slooshed around a boat in the ocean in it. Tried the different pad, no difference, went back to the Trail saddle and short of getting tossed on the ocean at least he wasn't getting -pinched or whatever the heck was happening with the barrel saddle.