Hello
and thanks for the response
i agree with you about CPU cores and HT
but i have another server with 2xX5650 (2*6Core-24Core with HT )
i assigned 24Core 
to a single Vm and it could eat UP all of the power when heis Resource Hungry and need Horse Power !
i wondered how could this possible that same OS and VM cant take more CPu
and about ESX need of CPU - i dont think ESX need that much CPU ( 1 real Core )
about disk speed yes you are right
sequential speed is far away from random access speed
but what about that server is under heavy load ( HDD random read and write)! and at the same time i started migration ! i must cant get high speed because disk is busy on random read and write ! but i get more than 100MBps Transfer rate at the time of migration but have IO wait on the VM ( at the migration time and normal operation)
about IO and buffer this server is a PictureHosting server and lots of request of various pictures are received by server ( it could eat up to 10TB BW each month for just 1 website)
one more thins i faced today is that after migration is that after i rebooted migrated Vm Centos detected filesystem problem on /home partition
what do you think ?
is this because of migration or real badsector on physical disk?