Should have some trials for these bots,if they cant verify the image for 3x they should be permanently banned immediately.
I've had captchas that took me longer than that to solve.
It wouldn't be a problem for the bots either. reCAPTCHA uses tokens to verify solving the challenge. Each token is valid for 2 minutes and is accepted for any captcha on that domain. So they have a server just brute forcing captcha solves until it gets a token for bitcointalk.org and then it can be passed out to a waiting worker bot to use. You'll never see a bot failing the captcha.