ASR1001 vs 1001-X PPP
Based on understanding, the CPU on 1001-X is more powerful and can handle more concurrent session establishments. It also has 2 10G interfaces which can come in handy. However, the queue-count is considerably lower in the 1001s which makes QoS difficult, depending on your policies. I would recommend a 1002-X if you are looking at ASR 1K.
Have a look at this document here for more details: