While this may not be the magic bullet for everyone it sure made a huge difference for us. Everyone is turning to the DB side which is logical but an OS change was night and day for us. We had MS in for an unrelated issue doing a Enterprise Health Check and they brought this to our attention.
We run 2008R2 SP1 for the OS on our box with SQL 2012 and perform all of our GIS activities against this.
By default the OS will be set to use 4k bytes per sector storage. Change this to use 64k bytes per sector. The downside is you will have to offload all your DB's to re-configure the OS and then re-deploy them but it was well worth it for us.
We currently have this single box and a single DB in SQL and it's handling over 1,000 connections, all the day-to-day user usage and editing workflows, a multitude of cross DB platform processes and ETL's with Oracle, over 150 ArcServer services (GP's, map, wfs primarily) and those support a variety of heavily used apps including our public facing web-mapping site and it hums along. We are working through implementing a second DB on the same box now to facilitate a massive enterprise deployment of Collector using AD FS integration and thus far still seen no performance issues.
Obviously, as many have discussed establishing your geom settings, dbtune configs and routine maintenance will be key as well. Hope this helps at least some of you.