You may be lucky, and your posts might of been saved in the drafts:
https://bitcointalk.org/index.php?action=drafts depending on how the forum handles the error codes. The forums slowness is unrelated to Tor though, and has been slow for everyone for the last hour or so but seems to be improving in the last few minutes. If it were a malicious attack, then the it's either stopped or the servers are now dealing with them.
I think it may be related. Since a ton of Tor nodes are banned by the captcha used by the forum, users tend to click on "new tor circuit for this website" until they find one of the increasingly fewer nodes that aren't been banned yet. This puts a ton of people using the same nodes to connect to the server, which coupled with the problem itself of the DDoS + increased organic traffic ends up in a terrible Tor performance.
You can always change the node once you manage to log in with another click on "new tor circuit for this website" but I think most people don't do that once they log in.