I have a client with 6600 databases. I now have them running efficiently on a single 2 CPU dual core 64bit box with terrible I/O underlying it. yes, they are small clients and they don't use sprocs (REALLY bad ADO code actually) but still I am amazed at how good SQL Server really can be when well managed. Actually, the PSS and CAT people at Microsoft were pretty stunned too when I told them my tale at PASS last year. 🙂
With that number of sprocs you have you could consider staying on SP1. SP2 causes a DRAMATIC reduction in procedure cache - which is great for most circumstances but could be disasterous for you with that number of sprocs. Test SP2 HARD before jumping to it if you aren't already on it. I would say that number of CPUs (real ones, not Hyper threads) will be key for performance to keep up with the compiles you are likely to be encountering - SP1 OR SP2. With 16+ CPUs I would also consider fibre mode. Consider reducing the min memory per query too and get REALLY familiar with memory management and analysis so you can watch and tune various things as necessary. As you mentioned increasing the worker threads may be necessary - note that there are DMVs for analyzing this too.
I found that with large numbers of databases virtually every tool I tried to throw at the server died a horrible death. Quest, Idera, ApexSQL, Embarcadero - all would blow up due to the overwhelming amount of metadata. The only thing I can use is SSMS! Log shipping/database mirroring is out too, so I had to build my own log shipping mechanism to do a refresh over to a warm-standby/reporting box.
The client was in the hurt locker when they contacted me and it took several months for me to completely eliminate all of the performance bottlenecks I could to get rid of their constant timeouts and server lockups. As a consultant I am thankful for the opportunity to have been able to work on such a system. 😎 We are now pursuing a scale-out mechanism whereby we will have client-database silos with 3-4K databases each that connect up to a primary 'global database' server housing the dozen or so databases that each client database needs to interact with. Fun stuff!!
Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
TheSQLGuru on googles mail service