Not that I know of. You'll need to tunnel through the proxy to really check the connection. I either do a proxy checker site to make sure nothing is leaking, or I just do the simple GET request against the site(s) I'm working with/on.
Are you sure? Cause normally when I try to do it on my own IP it says I am banned.
By accessing it through Proxy on ELITE proxies then it shows the image but then gives -1 status code.
Proxies are quite "pricy" and I doubt it would be worth it for me $$ wise :').
Do you know of any service with good/cheap proxies which haven't been used 1.000.000 times :-)?
Back connect proxies for me have always had a high fail rate they tend to be very slow, i have used the same services as you listed.
You have taken great steps to try and get over the problem I also increase the timeout limit.
I know it does not really answer your question but for me, i only use back connect for non-browser based bots as they work well.
Then for bots that require heavy lifting, i used dedicated.
Will keep an eye on the thread to get other peoples views :)