I have a vf52 love it. If you were to better it maybe spool alittle sooner although i think its got a great spool point already that if i dont want to be boosting i dont have to shift too early. And alittle more top end would be nicer.
I made 310whp 317tq on a really bad tune from my old tuner never been back to dyno since the Infamous tune. Ran a 12.91 @ 105.something on stock fuel.
Id say going to make a bolt on turbo that competes is going to require fuel mods so customers are just going to have to accept that or the turbo you produce to not require fuel mods probally wouldnt be worth it to most all in my opinion. Just because something alittle better then the vf40/46 is not worth $800+.
Dont know if thats any help at all or already your common knowledge but thought id share.