While I like the tension lower (mid-40's), I recommend that my customers start at the bottom of their racquet's tension range.
With poly, you won't get a lot of additional power from dropping the tension like you would with nylon strings. It mostly changes the way the ball pockets and feels.
USRSA MRT - Gamma 6004 + Wise 2086
K Six.One 95 16x18 - Pacific Prime Gut/Genesis Black Magic