Parallel testing of BO 4.2 with old 4.1 environment

Hi,

In order to test a production server 4.2 against prod 4.1 server, if both servers share the same databases via ODBCs,

will there be performance issues?

What is the best practice of decommissioning old server? All the reports we have are Crystal Reports. At a given time we may have 50-70 reports run daily.