we installed R720 esxi 5.1 dell customized server that replace our old R710
The r710 had X5660 CPU and the R720 have E5-2630 CPU
all other configuration and hardware are the same.
is there any reason why the R720 having hard time to catch up the R710 performance?
everything seems to work slower
Unfortunately that is like comparing apples to oranges. The hardware is different between the two. One uses Sandy Bridge technology the other doesn't. So it would be hard to answer that without a thorough understanding of your configuration.