75% throughput drop on Q1

In between build 1901 and 1909 N1QL throughput has gone down the drain.
On iris, Q1 throughput has gone down from 125k to 36k.
I believe the change is down to

http://review.couchbase.org/c/102597/4/cbauthimpl/impl.go#287

Please note that this issue is making n1ql slower than it was in 4.5 and is preventing me from diagnosing MB-32158.

FYI

http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=iris_650-1901_access_be02&snapshot=iris_650-1920_access_afb7

(sorry, I don't have the time to do a 1907 run, but from pipeline-daily, I know things went down in 1909 or prior:

http://172.23.123.43:8000/getchangelog?product=couchbase-server&fromb=6.5.0-1901&tob=6.5.0-1909
)

Any help would be appreciated.