As you are talking about override to give ranges in excess of 200NM I imagine the selection would cause the timegates to sweep through the greater range and, probably, the interrogator power output would be boosted. I'll bow to Graybeard's experience on the second point but it seems logical.
Certain Big Airlines used to operate with OVRD continuously selected which always seemed odd to me as there is little use for DME ranges in excess of 200NM and the selection would increase the chance of beacon saturation in busy airspace.
Added as an afterthought: selecting OVRD would also mean a slower initial lock-on, though not by much.
Last edited by Alex Whittingham; 2nd December 2006 at 18:47.