The "Close Votes" review queue has a substantial backlog. And, it's reasonable to say a queue consistently that large is unmanageable.
As per this test performed on the review queue, playing the numbers game didn't work. By increasing the review limit to 60, it only resulted in an 11% decrease in the "Close Votes" queue and the "Low Quality" queue had a 74% reduction.
Since there is a 1k reputation difference between the "Close Votes" and the "Low Quality" queue, the number of people capable of reviewing may be a huge contributing factor to why the reduction varied so much between the two during the test mentioned above.
That's why I think that reducing the required reputation to review items in the higher-tier queues can be a practical solution to this problem.
Queues for 3k rep can be dropped to 2 or 2.5k
Queues for 2k rep can be dropped to 1 or 1.5k
An alternative to this: Allow lower rep users to participate in higher-tier queues if they meet a specific pass/fail ratio for all of their audits and have passed a specific number of audits.
Of course, this could also be handled by the number of reviews a user made that were helpful.