I'm not sure about the need for a different voltage regulator, but I would suggest getting a good quality bulb. I've had good luck with Hella lighting equipment. It ultimately comes down to, you get what you pay for.
I recently installed a Hella Xenon +30% 55/60 in my 620 Dark. It's not brighter than the standard 55/60 that comes with the bike, but it's a whiter light that makes it appear brighter. Comparing it side by side to my g/f's 620 Dark w/original 55/60 (which is a Hella btw), you can tell the difference.
Hella makes a +50% bulb that has even more Xenon in the bulb which will be better yet, so I ordered a pair of them for our bikes. These are not gimicky "HID" bulbs either and are not tinted to give the look of true HID headlamps. So you won't look like a lot of the Honda sport compact guys that run around with blue headlights thinking a blue coated bulb is better than a standard white bulb. Here's a little info on the Xenon bulbs.
http://www.rallylights.com/hella/xenon_bulbs.asp
If I get the chance when I install the +50's, I'll try taking a picture of the lights shining on the garage door side by side to give you an idea of the difference.
I order all my lighting bulbs from here. Super nice guy and has most everything in stock. Shipping starts at $6.50 for priority mail though.
http://www.rallylights.com
Trent