Sorry. My knowledge is limited.
I personally haven't heard of any major security issues with IP. Cross site scripting within XSS is a concern for any forum, but I haven't heard of any MYSQL bleeding (or injections) on IP boards. Security architecture was written into IP, unlike vbulletin. If you don't have readable files on the server, you shouldn't have any security issues. At least in my experience. IP doesn't have an SEO engine, so I feel for you on that. But it appears that you rank for the majority of keywords I would think you want. Granted, my forum had just barely over a million pageviews per month, and I wrote my own plug-in's and supported myself. So I don't know the inner workings of having to have other people do it. Whole nother ball game for you my friend. Good luck in whatever you decide.