There was a recent degradation in a Jenkins performance test. The particular job is overflow-130k throughput. Read throughput dropped from ~800k to ~650k. The update throughput dropped from ~700k to ~600k.
The job showing the failure:
http://build.wiredtiger.com:8080/job/wiredtiger-perf-stress/plot/
The decrease appears to be related to the changes in WT-2439, since it first appeared in http://build.wiredtiger.com:8080/job/wiredtiger-perf-stress/2305/, which was a test on the WT-2439 branch.