Count custom objects with where in ACS, possible?

So, lets say we have a custom object defined with a certain custom field.

Is it possible to get a count for a query for objects with a specific value of this field? The "count" method on the custom objects seems to return ALL objects without being able to use a where for fields.

So what i can do it use the query method, and use count=true. But that returns max 5000 in the count. And even if i use something like sel:{"all":[]} i will receive an array with an entry for every object found...

I simply want a count for a specific field and no other data received.

Is this possible?