First - define performance horse. One county fair a year? Everyday all over driving? Multiple rated shows? Everyone's definition is different.
There is no magic feed you can give to make your horses better in the ring. I think a lot of people re invent the wheel when it comes to feeding horses. My mini stud that is shown at rated shows 5 or 6x in one summer does fine on just plain Jane nice Timothy hay. No powders, grain, special mash. Just hay and dry lot. He just does halter, showmanship, jumping, and trail.
My driving pony gelding that is barely shown needs unlimited hay and a bit of purina mini grain to hold his weight. However he's driven a solid 10 hours a week or so.
I would bump up the hay on the one that's too thin. 2 pound a day seems like way too little.