I'm pleased with the HiD my dip beam I got from Les Wasell through the site - single 35 watt HiD with H7R anti dazzle bulb. The smallish ballast is a doddle to fit and the burner gives a great lighting pattern putting the beam where you want it without excessive glare for our road users.
Les will give you any advice you want for a particular application.
Spanner
I have 50w on both dip and high beam on my 2005 1200GS (from Les W). The main beam does take 1 or 2 seconds to "warm up" but it's still bright enough when it first switches on.
If in doubt, go for a 50w dip beam. It's like carrying your own personal sun around with you...
His "plug and play" kits really are that. The instructions are brilliant, even telling you when to take a swig of tea...