Rock and a hard place. I'd go with 11.2r2, based on two criteria:
- It's on the train that has been identified as the next go-to release after 10.4r6/7, see the JunOS Rising content
- It's newer than 11.1r4, but not so new as to be untested in the field
You have SRX1400 today, so you really can't wait. But do monitor the 11.2 train, talk to your SEs, and see when it is deemed "stable enough to be recommended over 10.4r6/7".