I don't know the Cross sail, but I have TR sails from 6.6 to 11.0. I would guess the TR7 6.3 with little doubt, assuming the TR is rigged right. Be sure to measure the downhaul as directed on the Maui Sails web site (base of mast to top of pulley). All this assumes that you are in well powered conditions, 18+ knots.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.