Very slow acces to datastores on HP MIcroserver Gen8. Can't edit System Resource Reservation with vSphere client.

I performed a clean install of ESXi 6 with provided HP image (ESXi-6.0.0-2494585-HP-600.9.1.39-Mar2015).
Access to and from datastores over network through vSphere Client (6.0.0-2502222) is very slow - ~10 Mbps (  there are several hundreds under ESXi 5.5)
I'm suspecting that ESXi 6 limits CPU resources used by host system to 230 MHz.
I can't edit "System Resource Reservation" parameters (contrary to ESXi 5.5, where I can edit them and switch to Simple or Advanced view).