I would go with the collegiate or a wintec/bates. I have a wintec myself (bates is due in soon!). It doesn't take 30 minutes to change a gullet (more like 5-10), but here's the thing--you really won't need to change it all that much.
I leave mine on the medium-wide setting for my TB and my Paint, and just put a slightly cushy saddle pad on the TBs back. I have no back pain issues, and neither horse has a problem at all with being tacked up (and I ground tie because my barn isn't finished... no place to tie a horse! They'd let me know.) 90% of horses won't fit in anything under a medium, and the medium-wide is a good all-around fit for most horses. I really love having the flexiblity to change the tree if need-be--having a 1,000 dollar saddle that is always the same size is just too scary for me, lol! I usually change from medium to medium-wide as the show season continues and the horses build more topline--but the sweat patterns (and they) let me know when it's time to change.