How about function call overhead? For constructor and destructor no problem of course, but accessor wrappers will be called often, in fact it doubles the number of function calls for external access.
I would not worry about that too much. The potential number-crunching happening in your routines will most probably outweigh that small member calling overhead. If your methods are real lightweight (and they are defined in an included - not a linked - file) you can still rely on a decent compiler to inline them, bashing overhead to zero.
gr~~~