Roger can give you a more detailed response, but here are my thoughts.
Where is your mast base? I believe it should be in the front half of the track which will help keep the nose flat.
Raising your boom to at least shoulder to neck level, which will also help put more pressure on the mast foot (at 6'7", I hope the sail cut out will allow you to go this high).
Moving the base forward always requires raising the boom.
A seat harness will also help with "hanging in the harness" to add pressure to the mast foot.
With your weight, I would guess that you need at least 12-15 knots to get planing with a 7.5, so you should be seeing plenty of white caps.
Also, make sure that you are heading off a bit, 100+ degrees which will help keep the board speed up before you go for the straps. Get in the front strap first and keep the back food centered in front of the back strap(s) until you are comfortable and have sufficient speed, then go for the back strap.
Foot stap location may also help. Inboard and forward may help keep the board moving and flat in lighter winds, but outboard and back will help improve top speed and control in stronger winds. Were are your straps?
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.