pressure tank size

[Valveman]

Even if I use the existing pump with a CSV valve, I will still lose 40 psi, with a 50-70 set up that means I will be down to 10 psi before the pump turns on right? Probably not good?
Hef

Right!

The long multistage pumps that look like a submersible pump with a jet motor attached are probably the best you can do.

A Sta-Rite would be a model # 10SB75

Flint & Walling model # PB0516S071