There are 3L petrol X5s in manual or auto, I've converted a lot of them and these all run well, but the 3L is more difficult for the average installer to get good results on than the 4.4.
Someone phoned me last week to ask the same question as OP, answer was same as Gilbert's here.
Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
2 miles A1, 8 miles M62, http://www.Lpgc.co.uk