Incremental index time for 500M and 1B test of MOI is more by ~10%

Observed incremental index time 10% more in build 4.7.0-1550 build than 4.5.1-2844 and 4.7.0-1488 builds in showfast for 500M and 1B items.
Interestingly for 100M and 20M this regression is not observed, note that for 500M and 1B test vb_active_resident_items_ratio is below 30% for 100M test it is 100%.
Showfast link - http://showfast.sc.couchbase.com/#/timeline/Linux/secondary/incremental_moi
Jobs link:

500M - http://perf.jenkins.couchbase.com/job/secondary-moi/1262/ - time taken: 90.47min, 4.5.1-2844 takes 81.83min

1B - http://perf.jenkins.couchbase.com/job/secondary-moi/1263/ - time taken: 181.9min, 4.5.1-2844 takes 163.18min

Had a rerun on 4.5.1-2844 for 500M test - http://perf.jenkins.couchbase.com/job/secondary-moi/1265/ - time taken 81.83min
cbmonitor comparison URL for 500M - http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=nyx_451-2844_build_incrindex_1651&snapshot=nyx_470-1550_build_incrindex_db24

Log can be found in s3, link is in respective jenkins job's console output(at the end).