firstly, no it's not supposed to leak fuel from the overflow. That would indicate that either the needle & seat is worn, or more likely that the fuel float level is set too high allowing the fuel bowl to fill to the point that it, well, overflows.
Your other problem of appearing to run out of fuel at high RPM may indicate the opposite, that is that the float level is too low resulting in insufficient fuel in the bowl to supply the engine at high speeds.
Of course, your mate is correct, in that it is possible the fuel tap filter is clogged. I would imagine that the reserve tap filter would be in a similar condition as they are right next to each other. It only takes a few seconds to pull the whole assembly out of the tank for a look...
Cheer,
Andrew