Reddit reviews Philips H7 CrystalVision ultra Upgrade Headlight Bulb (Pack of 2)

Not exactly what you are asking, but I got these for my smart. They plug into the stock socket and are a lot brighter and whiter than the stock ones that were in there.

For $20 you might want to try them and see if they are enough for you before putting down a bunch of money and work for HIDs.

http://www.amazon.com/gp/product/B00480J4PU/ref=oh_details_o02_s00_i00?ie=UTF8&psc=1

Absolutely. I bought these Phillips H7s for my Mk4's high beams. There's an H3 option too which could work well for OP to have the same color temperature in every fitting.

Were USD$20 when I bought them, about NZD$25 vs $100 at a local retailer for similar but not as high quality bulbs. Even with express shipping to New Zealand still under half the price.