" I can tell you that the A300 Business class is OK. Not nearly as much legroom as their 747 business class, but the seats are wide enough I guess."
FSPilot747, You were probably flying on a A300 with the long-haul interior, which were mainly used to the middle east and to some destinations in africa.
Lufthansa also has A300 (maybe today only has, as A340s took over the routes to the middle east) with flexible Business/Economy Seats which can be switched from a 8 seats (2-4-2) to 7 seats (2-3-2) per row. These aircraft are used on domestic and european flights.
I am not sure if there is any more legroom as these seats are used as both Economy and Business seats depending on demand.
However, if it will be the A300 with the flexible seats which is very likely, the business class will not greatly differ from the C-Class on the A320.