I put a set of Warn lights on my truck last spring before driving to Alaska and have been amazed at their brightness, but they are also pencil beams. Warns website lists the reflective distance of the 160s that Tim mentions as only 235 meters, while the 510s that I bought reflect to 2408 meters (7900'!). The pencil beams obviously wouldn't be very good for slow speed wheeling. They sure are nice for the road though. Having had problems with glare in the past, I would avoid mounting on either the roof or the windshield.
For wheeling, my favorite light addition has been a pair of cheap walmart very small rice-burner foglights. They only cost $14.00 and are probably 2" in diameter. I have one mounted on the bottom of the radiator facing down to the front pumpkin, and another under the rear bumper facing the rear axle. If you get stuck rock-crawling in the dark, they are invaluable for a spotter trying to help you get out. Granted I don't use them very often, but when you need them they are great, especially for the price. You will probably want to upgrade the crappy wiring harness you get with them.