There is a known performance issue when using Couchbase Server 3.0.2 related to access() calls - I expect that’s responsible for some of the performance degradation you’re seeing. This is the main reason Sync Gateway 1.1.0 isn’t officially marked for compatibility with 3.0.2 (see http://developer.couchbase.com/mobile/develop/references/sync-gateway/release-notes/1.1.0/index.html for details).
I expect you’ll see improved performance with Couchbase Server 3.1.0, which is believe is targeted for release in the very near future.