How often are the lag spikes?

Do you have more than one AP on that SSID?

Is your AP set to auto-select channel? (if so, turn that off)

There is a note in the ISBoxer wiki (and I think a dialog warning you about it) where if you don't have your power profile set up to keep the CPU cores at 100% speed, you can see some of this.

The other thing that might be at play is the SSD. How old is it? I've had some very odd stutter issues when testing some Chinesium SSDs for work, and that magically went away when switching to Samsung drives.