Good news! AST 4100 coilovers are available via custom order through HP Autowerks for xi and x-drive vehicles!
After tons of research I decided to go with the AST 4100's once I found out they were available for xi/x-drive. I have a 2011 BMW 335i x-drive sedan. It is a custom order and takes 4 - 6 weeks but AST is building these by hand. I worked with Harold at HP Autowerks on this order. He is very knowledgeable on BMW suspensions and helped me build a custom setup. Once he gets the custom AST 4100's he is going to match them with custom swift springs. Harold thought I should go with 336lbs springs in the front and 672lbs in the rear. The stock 335 has 145lbs front and 460lbs rear. I could have went with 400lbs in the front and 784lbs in the rear but those are more for the guys who track there car. I just want crisp handling for spirited driving!
I was considering going with KW V1's or V3's but hear they squeak and have other problems. I was also considering the H&R coilovers but hear they have rusting problems.
Here is a great review of the AST's on a non x-drive 335i:
Link to AST Site:
Link to HP Autowerks: