Without rescue craft I would stick to 15kts or less. It will be a handfull at 15kts but manageable. 15 over things start to happen much more quickly and I found during my adapting from monohull to cat it was being too slow or unable to predict the boats reactions that caused the most problems.
My hardest habbit to break was rounding up when in trouble. When pointing its fine but when reaching at speed its more likely to capsize you from the force of tunrning the boat causing it to kind of trip itself up and capsize. When your in trouble and about to capsize release the main and steer downwind dont round up.