SpeedySQL (4/17/2014)
If you're considering upgrading to SQL 2012, be aware that the licensing model is changing to per core. Another factor you may want to look at apart from maximum RAM is whether you need any of the Enterprise-only features. If not, the difference is cost is quite big to do it just for the RAM limits. You would be better off having two servers with 64GB of RAM running Standard than one with 128GB running Enterprise. There are subtle performance-related benefits to take into account, however, such as the automatic use of indexed views by the query optimizer. Also, be sure that you're OS supports your desired amount of RAM - are you on Windows Server 2008 R2 Enterprise?You can see a comparison of the different versions and features including costs here -
SQL Server Version and Edition Comparison[/url]
As for metrics to look at when evaluating the upgrade, this is a good article on measuring memory pressure by Jonathan Kehayias - Great SQL Server Debates: Buffer Cache Hit Ratio[/url]
I think you'd be better off with two SQL instances on a single server with 128GB, which is the point I was making earlier.
With 2-node clusters now being a part of standard licensing (at least last I checked), many places no longer need Enterprise except for RAM usage. Therefore, I suggest looking closely at CPU licensing and using multiple Standard installs on one server (with a single licensing cost, since they are on the same CPUs) vs a single Enterprise install, since Enterprise is much more costly.
SQL DBA,SQL Server MVP(07, 08, 09) A socialist is someone who will give you the shirt off *someone else's* back.