We have few 64 bit servers and 32 bit servers. We didn't find any performance difference on 64 bit boxes and 32 bit boxes. Are we missing some thing here? Our applications use mostly 2-3 gb ram. If we use more than 4 GB, would it show the difference performance?
Well they aren't designed to show a lot of variation. The 64 bit can generally take more on and is more reliable, so if you were making a choice, i would go with the 64 bit servers.
By simply upgrading the OS to 64 bit you might not see a performance increase. First understand a 64 bit OS simply allows a 64 bit application to address more then 4GB previously 32bit's limit. So if your application are not addressing the larger RAM you will not see an increase in performance.
By all means if you can get 64 bit servers go to them. Even if they are not showing performance benefits now, they will in the future. Plus they can access more than 4 GB of RAM as well.
Well they may not be developed to demonstrate a lot of difference. The 64 bit can usually take more on and is more efficient, so if you were creating an option, i would go with the 64 bit web servers.