How Slow Is Slow? Proxies

I just opened Tweet Attacks and got prompted for an update. Among the updates I found one feature that will be helpful in managing proxies. The feature allows you to automatically delete slow proxies. However I really don't know how slow is slow. It allows you to choose what an acceptable time in milliseconds. So what is a good time that is acceptable?

keep anything below 2/3000 ms

Everytime I harvest and check proxies I make sure the response time is 5000ms or less. It's annoying how many proxies seem to just burn out, but then again I guess that is just part of the Black Hat game...

Thx peeps