I'm trying to do the same thing.
https://github.com/NodeBB/nodebb-widget-essentials/blob/master/library.js#L234
If only we could pass the current category here, it shouldn't be to hard I think.
I know that @scottalanmiller is running a relatively high traffic forum on nodebb.
A lot depends on various factors like if you're running a CDN, what plugins you're running, and any other processes running on the node.
On my setup, I was running a cluster of three, with a gocamo server, along with redis (for session storage) and mongo, along with (at the time) mysql.
