GE's 7" round (H5024?) (available at Wal-Mart or many FLAPS) is the way to go.
It's a long-life lamp, and the closest thing you'll find to a true "high output" 7" round.
Sylvania's SilverStars are nice, too; but they use a "blue" bulb to make the light whiter (not brighter), and are significantly more expensive.
Relays are a nice touch, but usually not necessary if your stock wiring (including grounds!) is in good shape.
There are no 6V Halogen 7" round headlamps that I know of; and last I checked GE was the only one making the incandescents domestically (the GE bulbs are also boxed for and sold by other brands.)
Don't worry about relays, just make sure all of your connections (including grounds) are clean; and use the "light bulb grease" on the connections when installing the new bulbs.
Cheers,
mark.
