I bought a couple more MR16 LEDs from here
eBay UK Shop - IT Global Solutions: Lighting, Bathroom, Kitchen
These have 24 LEDs each and are rated at 1.5W. I found that at 15V they take 100mA so I used a LM317T to drive the two in series. This gives me 3W of light and they are also more directional than the others so they light up the lane nicely and also throw out enough to the side to light up the kerb/hedge etc.
I also notice that some rain got into the last bulbs. I think this is because the front glass is not sealed to the body, so I ran some super glue around these to seal them.
I had to make a new bracket for the two bulbs, like the last but with one on top of the other and a little higher so that I don't get as much shadow from the wheel.