ipsec encapsulated gre tunnel between two RB951G-2HnD max speed is 520 kbps

Hi,

I have setup a gre tunnel encapsulated by ipsec between two mikrotik board.
Connection working fine, ping response times are also fine but when we start the
copy process over this tunnel (gre is established over internet connection)
the copy performance cannot hit more than 520 kbps. How can I imporve this
performance? (I use routerOS version 6.31 on both devices) Is there a limit
somewhere? CPU usage is does not hit 10% on both end. Memory usage is
also not an issue. MTU and MSS is set to automatic adjustment.

Thanks for help,

klajosh2