Robert_Charlton - 5:30 am on Jan 12, 2013 (gmt 0)
Google has an excellent support page on various pagination options you can use for your situation (viz, 'sequential urls for forum discussions')....
Pagination - Google Support
For a forum, where you often can't know where in a thread your good posts (or your most relevant posts) are likely to fall, I myself would use the option of specifying a View All page and using the rel="canonical" link as well.
As the article describes the setup...
Specify a View All page. Searchers commonly prefer to view a whole article or category on a single page. Therefore, if we think this is what the searcher is looking for, we try to show the View All page in search results. You can also add a rel="canonical" link to the component pages to tell Google that the View All version is the version you want to appear in search results.
Other options described include doing nothing and letting Google figure it out, or using rel="next" and rel="prev" links. Again, because of the unpredictable shape of forum discussions, I would go with the View All option. I'm assuming that with the canonical link, this option would allow you to use any post count you like.
There's also a 16 min video that goes through all the options. I think it can be particularly helpful to see after you've read the support article (and in fact it's linked to at the top of the article)....
Pagination and SEO - Maile Ohye
Mar 12, 2012