I actually like the multiple database notion for such scenarios. With a good naming scheme you can automate the heck out of it, including view (with UNION ALL) modification, data...

1) Please provide create table statements, INSERTs for sample data, and expected outcomes that cover all logic paths.

2) Review OUTPUT in Books Online. I didn't read closely, but...

Here's another example from my Common TSQL Mistakes session (originally from Plamen Ratchev):

Use tempdb
set nocount on
go

IF OBJECT_ID(N'Accounts', N'U') IS NOT NULL
 DROP...

The optimizer can do (almost) anything it wants with your query as long as boolean and algebraically it still gives the same output or effect. Predicates can be pushed up...

If you have sufficient memory and poor IO then buffer pool cache could be some of the reason.

Best is to repeatedly run sp_whoisactive during any long-running processes to...

If that oh no was related to not being able to use table variables note that you REALLY shouldn't use them. No statistics means...

SSC.com's own Grant Fritchey wrote the book on the topic, and it is FREE:

SQL Server Execution Plans, 2nd Ed.

There is plenty of CPU and Memory when this happens. So...