I know of both Tushingham, Carves and S-type.
Probably you have a 430 mast for your current 5.5 Tushingham sail.
The biggest you can get for this is a 6.25 Tushingham Storm. The new Tushingham Storms are excellent for your purpose (as a lot of other brands are) and it will probably take almost as much wind as your old 5.5. Especially if you go to a smaller board than your start and you add that downhaul.
The S-type i a lovely board for an advanced windsurfer. It's not the next step from a Start.
A not too old Carve in D-ram will give you a lot of pleasure. I've had several and they were all early planing, easy to control and surprisingly fast. Get a nose protector if you are not too safe on your feet at the beginning.