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.
source: TENAA (translated)