The issue is not " are same files on same computer work slower in 64 bits?" , is "how many days until load is too high for 32 bits?" . That is the moment when random programs die with "out of memory" = server is unreliable.
I am also trying to get a feel for what would be a reasonable specification/cost. For example, if a 64Bit system with 12Gb RAM and similar CPUs as my 32bit environment gave me the same level of performance as I currently have, then I could reasonably ask for 24Gb RAM/better processors to improve performance by a factor of 2.
So, I guess my question is 'what are the relative requirements of 64bit compared to 32bit - 2x RAM? 10x RAM? More processors?'