My forum has indeed been very bogged down since installing, but we did have some pretty high traffic so it seems that would be more likely the reason. Optimise has saved us 4.4 million queries in just a few days.
I see this feature in the Pro version:
Full Guest Caching
Ability to cache entire pages and serve them saving not only hundreds of queries but upto 90% of CPU processing towards Guests.
This may be what I'm looking for since a lot of our visitors are guests. If 75% of our visitors are guests, would you be confident that this "90%" savings in CPU usage from guests would be our solution? I'm looking to upgrade the server but considering trying this first. Although the server upgrade might be cheaper.