Good idea, but it has a few problems. I dumped 204,000 raw proxies of all types (Elite, anonymous, transparent, Google enabled, not G enabled, sock 4 & 5), 5700 known to be good. 589 that would work in the scraper that I use. The checker promptly choked. It took quite a while to load the proxies - far longer than it would to download them from the program I use. I set the threads to 100 and the timeout to 60 and launched.
Here are the first few entries from the valid file:
:3128
:443
:80
:8080
:8118
Notice that the entries are only the ports. After those bad entries from properly formatted IP

ort entries, the program began to work but only picked up 43 good, of a known 5700 good, proxies. After checking 1838 proxies, the program seized. The program on a large proxy set also read the wrong number of proxies (44000 when 204000 were loaded). I rebooted the computer three times and reran the test. Same result each time. On a much smaller set of filtered proxies, the program appeared to work properly.