[StreamRecorder]

• On spinning HDDs, pre-allocate the entire virtual disk. On SSDs, it doesn't matter.
• Allocate only the storage you need. Keep large files elsewhere, outside the vStorage.
• Never allocate more CPUs or RAM than you should. 1 vCPU is probably enough.
• Leave 1GB of RAM for the HostOS. Do not over commit RAM.
• Use the VirtIO drivers for Storage and Networking. Modern Linux guests support this. For Windows guests, use the SATA (storage) and Intel PRO/1000 (network) drivers. It is possible to use virtio drivers under Windows, it is just a little harder.
• Enable ACPI and AHCI for all guests from 2003, WinXP and later.
• Desktop VMs should get all 128MB of display vRAM
• Server VMs should stay with 9MB of vRAM; don't waste it.
• Avoid 2D and 3D accel settings, until you have everything else working the way you like. I'm serious. Ubuntu does bad things when this is enabled. It can bring a Core i7 to the ground.

Source: http://blog.jdpfu.com/2012/09/14/sol...-in-virtualbox

Currently I use:
RAM: 840 MB
I/O APIC Enabled
2 CPUs
PAE/NX Enabled
VT-x/AMD-V Enabled
Nested Paging Enabled

VRAM: 128 MB
3D Acceleration Enabled
2D Video Acceleration Enabled