The throttle plate in a E36 325 and a E34 535 are as near as dammit the same diameter ie. 65mm, and it is only a minor restriction at high revs on the larger 535 (stock).
On that basis I reckon a larger throttle body will be no use at all to you unless you increase air flow dramatically with big cams etc. like Markus says.
A bigger throttle body on a stock engine will probably result in a loss of low and mid range torque.

Bill G