GTM Pool for external proxy site

We use an external proxy provider; we experience severe latency on a fairly regular basis. I would like to create a GTM pool with each individual proxy site as members in the pool, I would like to run a GTM monitor to each proxy site to measure latency and/or availability.

 

1.1.1.1 - Site 1 = 120ms 2.2.2.2 - Site 2 = 60ms 3.3.3.3 - Site 3 = 88ms

 

etc., I would like for the GTM monitor to measure the latency to each site and make load balancing decisions based on the latency/availability of each site. In the above example I would like for all requests to get sent to Site 2 (lowest latency). I have never done anything like this before; I though maybe using a script GTM monitor that calls some file referenced in the iFile list but am unsure on exactly what I would need to do. If anyone has any knowledge or experience with this type of setup your insight or assistance would be greatly appreciated.

 

Thank you, Damon