Requests through the proxy external IP, returns timings. First colon - time to connect to proxy, second - overall query time, third - difference, fifth - external IP. Time in nanoseconds.
Usage example:
pxcheck 1.2.3.4:8080
130223411 192210200 61986789 1.2.3.4:8080 8.7.6.5 wgetip.com