(My opinion) lights on the cab work well in the yard.  In the field it's like using high beams in fog.  All it does is decrease visibility.  Plus anything in the path (mufflers, air cleaners, hoods) creates a distraction.  On the back of the cab I'd make it on a separate switch to turn off of I wanted.

One odd idea I'll toss out there is keep the original headlights lights for going down the highway.  These will blind oncoming traffic.

Oh, and take your heart medicine before you check prices.  Good lights are not cheap.

I'd suggest a 50" light bar out front, 

20" ones on each rear fender,

and 6 or 9 inch quad lights on the fenders and rear of the cab.  we put 6" on our fire trucks and have been VERY pleased with them  Note these are switchable spot or flood.  We tied the wires together and run both at once. On the rear of the cab being able to switch might be a good thing

We got our fire dept lights from superbrightleds.com and been very pleased with them