I have not personally used SimplePress or bbPress with exceptionally large installations, but there was previous discussion going on at https://bbpress.org/forums/topic/bbp-plug-in-for-wp-scalable 
Thanks Jaredatch,
So the WordPress support forums have been around for as long as I’ve worked with WP. Well after that though, bbPress was still in standalone form, thus a different database. Is it better to have a site with lots of posts and comments (essentially posts) on the same database as the bbPress forums? (essentially posts)
It really just depends on what you want to do.
bbPress 2.x isn’t going anywhere, so if you are considering moving the bbPress that’s likely the route you will want to take.
You likely won’t encounter any problems, even for a “large” forum. The only time (from what we have seen in the past) that issues have come up is when various caching methods are in place.
The main reason there is no “definite” answer for this is because at the moment there just aren’t a lot of large bbPress installs out in the wild. If there were more we would be able to address some of the issues (like conflicts with caching) but they are so few at the moment that it just makes it hard to track down.
If you don’t have a forum yet, now isn’t the time to worry about if it will scale.
Scaling is about spreading the pain around. As you outgrow one technology (or set of technologies) you upgrade to another as needed, not as predicted or as planned.
This isn’t to say you shouldn’t have a plan, but it’s awful early to know if it’s worth the time spent worrying about.
If you’re 100% certain that you’ll have +1million posts a year with billions of hits a month, then you wouldn’t be asking this question because you’d already know the answer: no, it won’t scale out of the box; you’ll need caching, memcached, and countless servers and data centers to manage it all.
The short answer, don’t be afraid to start out small. When it’s time to grow, you can pretty easily export specific post types with WordPress’s export tool and shard it across multiple multi-site blogs if you wanted; shard the database(s) across multiple servers; whatever you need to do to get by.
If your forums grow quickly and you find performance gains, it’d be great to have them contributed back to the project. It’s true that moving from bbPress standalone to plugin traded some performance for convenience, but it’s been the # 1 most requested feature since it’s introduction.
Also, there’s nothing *wrong* with bbPress 1.1. If you’re more comfortable using something purpose built from the ground up as a simple forum, you can still use it. Just know that nothing but fairly significant code changes or bug fixes are actively going in.
Thanks again Jaredatch and JJJ. Very good insight.
The site’s forum will pick up and to a pretty fair degree soon, which is why i thought to plan ahead. But you’re right, one step at a time, and revenue generated in relation to the number of posts/forum popularity will make it easy to remedy any performance problems like you’ve mentioned.
I’ll be using W3TC, as I do already on the site. So I suppose I’ll be looking in on how to best optimize it for use with bbPress.
Thanks again gentleman.
