Join Date: Oct 2007
Location: Greenville area / SC
Pictures would be an enormous help. We would also need to know the bar size on the saddles you have been trying.
To answer your other questions, "Yes" sweat marks are an important indicator on how your saddle is effecting the fit. Depending on how your new horse was fed and conditioned and how he will be fed and conditioned by you, he may change his physique. Personally, I would not invest in a new saddle until you see how that goes unless it is so far wrong that it causes problems.
My current horse was 11 when I got him last year and after ~6 months, his weight and muscle improved so much that the saddle that worked for him at first no longer worked.
I'm not arguing with you, I'm just explaining why I'm right.
Nothing sucks more than that moment during an argument when you realize you're wrong.
It's not always what you say but what they hear.