The 8.5 or 8.2 NP's on the GO 155 should be just the ticket to get you planing alot more of the time.
Get a bigger fin than the stock fin and you may be amazed at how fast and fun the Go 155 can be..... esp when all the other sailors on narrower boards cannot get going.
This is like Ken with his Formula.
He planes pretty much every day he sails.... why... 100 cm wide Formula board and a very big sail.... I've seen him!
But, as soon as the wind gets up a bit he will change down to the iSonic and smaller rig (unless he's in training for a race on the formula).