As fusioneng says, partially furling the sail as wind increases is a good idea. You will be surprised how effective the sail is even if half is wrapped around the mast, in stronger winds. BTW, I wouldn't agree with him that the Island is not a true sailboat. It is indeed quite possible to sail an Island without using the Miragedrive, but why not use it as it is at your disposal.
In stronger winds, I find myself pedalling like blazes to keep boatspeed up throughout the tack, even after applying the usual sailboat techniques of bearing away slightly to increase speed just before the tack, and if there are big enough waves, accelerating down the back of the wave into the tack.
And of course, if absolutely necessary, you can take the "easy way out", and once you are pointing straight into the wind, in irons, point the tiller in the opposite direction to where you want to go, and the hull will swing round pointing the nose in the direction of the new tack as you begin to move backwards. You might find this manouvre easier if you temporarily ease the mainsheet until the nose has gone across. This method won't win races, but that is not what Islands are designed for!
2012 Tandem Island "SIC EM"www.scenefromabove.com.au