IMO Save the money from getting a 5D or 1D3, get a 40D or used 1D2 and a whole slew of L lenses. Remember, the camera body is useless without the glass.
Plus it'd be pretty.. off.. if you bought a damn good camera but become limited by your lens range, no?

BTW a jump from a 350d kit right up to a 5D or 1D3 is a wee bit drastic, no?