According to China's Telecommunication Equipment Certification Center, which recently approved a TD-LTE version of the Lumia 640 XL, the handset comes with 2 GB of RAM, and a quad-core processor clocked at 2.2 GHz (this is definitely not a Snapdragon 400, but it's not clear what model it is). These changes should obviously make the China-bound 640 XL a superior device. The rest of its features seem to have remained unaltered, thus including a 5.7-inch 720p display, 5 MP front-facing camera, 13 MP rear camera, and 8 GB of expandable storage space.
Microsoft will release the Lumia 640 XL in April, for prices starting at around $220. We don't know if the more powerful version of the handset will be available outside of China, but we're going to let you know when we find out.
Microsoft Lumia 640 XL
source: TENAA (translated)