All i know is that i had a standard ebay Led 5watt bulb in there and its ok..
Ive seen new led bulbs called Cree led, which is a better led bulb and a bit brighter. get something 10W maybe?
This seems to be alright:
10W CREE LED Angel Eye Halo Ring Light Bulb BMW E39 E60 M5 x5 x3 E53 E63 E64 E65 | eBay