FWIW; Increasing the speed of a shotshell isn't going to improve the reach. Increasing shot size and payload will.
Winchester has loaded a 1oz load in the 28ga for many years. I can even remember reading some magazine articles written by Jack O'Connor about using the 1oz 28ga load for hunting pheasant with John Olin.
I've used an equivalent load from the 28ga but only for shooting squirrels and once for wood ducks back before lead shot was outlawed for waterfowl.
In the 20ga, my "go to" load has always been a Remington SP20 wad and 1oz of shot over 16.0gr of Unique. 15.8gr of Universal works just as well.
For both the 28ga and 20ga, I use LongShot now, if I reload. It works. For no more than I shoot shotguns anymore, I just use factory ammo. Lately I've been shooting a .410 o/u and will from now on use it for quail, ect... Only for waterfowl will I pull out the 20ga and I might as well sell the 12ga for as little as I shoot them.....
I too suggest you go to
www.alliant.com and
www.hodgdon.com for your hull/wad/powder recommendation.
If it was me, I'd just use the same load you've been using with #7.5 and call it good. 1/8oz of shot and 100fps ain't gonna make any difference....Changing from an improved cylinder choke to a modified choke WILL make a difference. If you need more than a 1oz load of #7.5 for quail, get a 12ga and shoot the 1-1/4oz #7.5 3-1/4dr eq. load (1,140fps). If this won't work, quit while you're ahead.....For me, the 1/2oz #8 is splendid for quail, and not "overkill" when hunting the pen-rasied birds.
My older brother was stationed in Alamagordo, NM back in the '80's. He was "broke" and his only gun was a Winchester M1300 pump. He used a 1-1/2oz load over a light charge of Unique from the Winchester AA-Red wad for everything in a 2-3/4" AA hull. Only changed shot size for different game. He said it probably chrono's only ~1,000fps. It went "poof" instead of "bang" as he put it, but it was "death" on the Gambel's and Valley quail as well as Hungarian partridge and grouse he hunted with an english setter....even if they got up at 40yds or more....