This is the saddle and pad/blanket I have used on her for the past year or so. I'm going to order a larger neoprene girth in a couple weeks for her. I do not like that one pictured.
I'm trying to figure out if she needs a narrower tree. It looks like there's not much wither clearance. She has low withers and she's fairly broad. Let me know what you think about the overall fit from the pics.
Offhand, it doesn't look all that bad. It would be best to see its' fit without any pad on at all, and a shot that is kind of just off the shoulder, so one can see the front edge of the tree. It looks like a rather old saddle, but well made.
I should say, I can't really see very far into the area under the fork (horn), and so maybe it is a bit tight. When you are mounted, can you get some fingers inside there? That is the real teller.
Tiny, next time I am out there I'll get pics without the pad. I am proud of that saddle. I've had it since I was 13 and got my first horse. I researched the serial numbers and found out it was made in about 1943. It is a Bona Allen and very well made. The only work it's had done is new fenders because my old mare ran one side into a fence and tore some leather. I was much rougher on my tack then It's held up really well.
I think I might be able to fit just one finger under the gullet after I'm mounted. I use a thin pad then that blanket on top. I'd like to get a better quality pad eventually.
The fit doesn't look too bad, though its hard to tell with the pad. It may be a little snug, but I'm not sure you would get significant improvement with a different size tree - the gap between semi-quarter horse and quarter horse is significant and you might just end up with a saddle that looks a bit too wide.
As long as you are padding well and your sweat marks are even without any dry spots, you should be fine.
From the pictures, it looks like it fits her good. Your saddle does not look 'perched' which would be a sign of it being too narrow and it is sitting pretty level so that is sign it is not too wide. It is not too long for her back and overall looks good. Your new longer girth would be good for her comfort and your stability.
As far as wither clearance, as long as when you are sitting in the saddle, there is no pressure on the withers when you are sitting in the saddle, I would say it is not too wide.
Basically, 'air is air' , so if it is not touching her withers when you are riding, 2 inches clearance or 4 inches clearance is the same thing.
In general, a thicker pad makes your saddle fit a bit narrower, a thinner pad makes your saddle fit a bit wider.
You can see the saddle in my profile pic is too long for my horse, so I have to put it up too high on him thus limiting the movement in his shoulders and it is a bit too narrow, so it does not sit level.
His dressage saddle however, which is an xxwide fits him (and me with a 36" inseam!) perfectly all around in wither, back & shoulder: