There a few things that make things appear as they are. Correct me if I got something wrong:
- HyperThreading appears as two additional cores on your dual-core CPU but will not act as real cores. HT will give you a maximum of 30% performance gain and 10% in real world applications. Full load on your Windows host will never show 100% load on each logical CPU in task manager. Task manager may also hide kernel-space load and only present user-space load.
- You have presented two logical CPU:s to your VM, which will amount up to 50% total system load on the Windows host.
- Assuming that 100% load on the guest equals 100% load on each presented logical CPU, you will cause 50% total load on the Windows host and with other things also running, apparently 68% in grand total.
I've been fiddling with virtualization, Windows and Linux for some time (even professionally) and HyperThreading is always causing questions like this. The issue is that new logical cores appear that do not appear to have the same power as proper cores (poor explanation)... Another example is the opposite where the message is that the new CPU:s were so much faster that total system load is only about 50% while the load really is 100%.