1 - If you use Sync Gateway only for the mobile and Couchbase Server only for the web application, you have the speed but you do not have instead the web site RBAC.
You will also need to use Bucket Shadowing to keep the Sync Gateway bucket from getting corrupted, which adds complexity.
1 - To update and delete you have to use the revision_id
This shouldn’t be that hard. What’s the issue you are running into? (just makes your code more complicated?)
2 - You lose in speed, because as I noted CouchNode (I use Node.js as a server-side language), is much faster than HTTP.
True, the memcached protocol that is used by the client SDK’s is more efficient than HTTP. With HTTP2 around the corner, this gap may narrow quite a bit.
Can you be more specific regarding the speed issues you are seeing? How may ops / sec are you trying to run?