I tried 30 pounds with Ashaway kevlar 16g on the mains and a synthetic 16g string on the cross. Its totally playable at this tension. I think a poly string is the way to go though for less string movement.
Wilson BLX 90 - Wilson Pro Overgrip - 12.9 ounces
Wilson Gut 16 / Luxilon ALU Power Rough 16L 51/51 pounds