Hi. I have a few more suggestions about your spam problem. Are you banning e-mail providers? I can provide you with a list of what I have banned as well as some creative use of "wild cards" in banning people. For example;
(lol....that looks like a viable site) becomes banned with *@*drugs* You can also ban providers with names that contain phentermine, viagra, porn, etc with the "wild card".
Banning IP's is problematic. Most spammers have dynamic IP's anyway or operate from hijacked computers so banning IP's is often a piecemeal solution.
We run our board off of SMF (simple machines) which we switched from Yabb about a year ago. We have relatively few problems but we are a much smaller target (only about 40K posts). I am a real "nazi" about getting rid of spam; kind of a "kill em all and let God sort it out" proactiveness.
In addition to banning e-mail providers like .ru or .gawab (and there are many others) I would suggest you "enable" 2 features I imagine that this board has but are not enabled; The 5 (the number is defined by an admin) last post topics and who posted them, ALSO you may also have enable "show recent posts" perhaps up to 10 pages with 10 posts per page with info on the post topic title, the member who posted it and the actual post. With these 2 features enabled your mods should be able to hunt down recent spam far easier and delete it, and smite the wrongdoer.
Also even if your mods don't have "global moderator" (like a light weight admin) they could still move an offending thread to an out of sight board. If your mods can't keep up you can also just add a few more. You have a big forum and you may be stretched too thin.
One other question is when your board was last updated? Yabb may have some new spam fighting mods built into a more recent version.
If there is anything I can do that may help let me know....