Assuming you're monitoring your servers, you know that server X is under some stress for CPU and this new app looks like it might have lots of recompiles, so it goes on Server Y. You need to know what your servers are doing and what the apps are going to do. This involves monitoring the servers and testing the applications. Then use the numbers in hand to make decisions. Further, Server X is Enterprise and Server Y is not. Does your application need Enterprise only options? If so, it's going on Server X, if not, Server Y.
"The credit belongs to the man who is actually in the arena, whose face is marred by dust and sweat and blood"
- Theodore Roosevelt
Author of:
SQL Server Execution Plans
SQL Server Query Performance Tuning