Assuming your 350 is now shooting where it should (lower-mid 800's at the muzzle), let's figure an average of something around 750fps over a 40 yard distance. That gives a flight time of .16 sec, which translates into a drop of about 4.9".
If your gun now shoots 7.5" higher than before, that means it used to have a total drop of 12.4". That translates into a flight time of about .25 sec, or an average velocity of around 480fps. That looks like it'd be in the 500's at the muzzle.
Now you have a rough idea how much you gained: a sh*tload.
I'm kinda keeping track of how much Diana breakbarrel owners gain by properly shimming their seals. Prior to that my .22 Panther was the champ at gaining 140fps (600 to 740). You just beat me by quite a bit.
I just hope you didn't damage your gun - a seal like that is almost a dry-fire. But considering that it now seems quite healthy I suspect you've got nothing to worry about.
