I’m managing a bbPress 2.5.x forum with 10K+ users, 25K+ topic & 200K+ posts. It’s actually pretty fast: https://saabklubben.se/forum/
I’ve tried to minimize the number of plugins. The bbPress related ones are bbp style pack, bbPress – Report Content, bbPress Notices, bbPress WP Tweaks and GD bbPress Toolbox. However, our forum is a part of a Multisite network with 50+ active plugins (BuddyPress, WooCommerce, WangGuard, Akismet etc).
There has been some optimization done here as well. We’re using GeneratePress, which is an excellent theme in terms of performance (and much more). The optimization plugins are primarily Gator Cache, Autoptimize and EWWW.
On the server side we’re using Nginx with MariaDB and PHP-FPM (PHP 7). We also use Cloudflare and Redis. But it’s a single server setup, with ServerPilot and DigitalOcean (16 GB droplet, but we could easily use a 8 GB droplet instead).
In my experience, the best things we’ve done for optimization is to use PHP 7 and Redis. Those things have had the most impact on our performance.
