[Bob_Young]

Gamer, to answer your original question, get the L4400 for sure. The L3400 should not be even remotely considered for mowing 400 acres. But even the L4400 will have to stretch for that application. Like the others have said, 70 plus HP and a 15' batwing might be needed to keep the job from becoming a full-time occupation. Whatever you buy is going to burn a lot of diesel mowing that many acres. At today's prices, you're going to need a day-job to keep the tractor fed. Can't do that if you're mowing all the time.

With that much field work, I'd get gear instead of HST. It's simpler. You don't have to ride a pedal or mess with cruise control. Just pick a gear, set the throttle, and go. If you come to an easy stretch, just push it along a little quicker with the foot throttle.

Only time an L3400 might be preferred is if you're doing a lot of work in tight quarters around obstacles or for lawn work. Doesn't sound like that's in your plans.
Bob