Most things have already been covered, but just to correct a small error. Ions are LP makers not HP.
On topic. Try to find out what pressure is better suited to your marker. I run an ion and a 05 ego now both require different pressures to work at their best, but i am blessed as i own a crossfire LP reg and it can cope.
So either get the specific type for your marker or get one with a good quality reg like a crossfire or cp stubby.
As has been said neither hp or lp will affect the velocity or trajectory of the ball, unless your ramping at a high rate of fire when lower quality tanks of the LP variety will struggle to maintain a constant and even flow.