Yep... HID is what u need. A 35w HID will giver 2.5 times the light and a 50w HID will give you 4 times the light.
A twin filament bulb sounds like the best you will get is twice the light, and you are going to have a major problem cause at least one of the light sources (or both possibly) is going to be in the wrong place relative to your reflector ... meaning the light wont focus properly.
Just fitted a pair of HID units to my 2006 1200gs - stunning! Bought them from ww.hids4u.co.uk in Leeds - cost a couple of hundred quid but the difference is amazing. I bought brackets to fit the ballasts from the US - I will post the site later. Fitting took around an hour - the most time was taken removing the beak and screen to get to the connectors.
Av a word with colebatch mate .I bought a set of 50w hid's from him and boy are they the biz....an hour to fit on 1150 gs .E-mail colebatch aka walter above..