The big difference in a separate table would be you would only be doing a single quick lookup based on user ID and forum (the adding would be done at post time) -- no scans or counting. With the current method, it has to scan each table entry and add them up (in my case, 1,000,000). So 1 vs 1,000,000 is quite a difference.

Another way of looking at is with a separate table, in my case, there would be at most 11K entries (one for each user) with one row as a result. Currently there are 1M posts with possibly thousands of results needing to be counted on the fly.
Of course the current method is available now, and a separate table is more like an addon to the software than just a quick mod.
Thanks for your help in any case and I'm sure some users will find it useful!
-vissa