I would probably lean towards the conquest but in the 44mm not the 50. The 50's will be mounted waay high and it will be tough to get a good cheek weld.
The conquest also has the side parallax adjustment which is handy if you are trying to wring some long range potential from the big .338's. If you ever have to scabbord the rifle I would lean towards the leupold as there never seems to be enough room in the scabbord for the extra side focus turret of the conquests in the scabbords I have used
The VX3L will of course be able to mount a little lower but that front lens with the screwed in retainer just never looks as robust to me as the normal round threaded in lens retainers on a more traditional scope. this could become an issue with the somewhat stout recoil that could be generated by a .340
That said both of these are great scopes and you can't really go wrong between them