I know quite a lot about PWM voltage regulators
Hmmm....well, you forgot the extra needed capacitors...should have two electrolytics (6.3V, at least 2200uF...I would probably use 3300uF caps) from the output of the coil to ground (CPU VCC plane -> ground) or else the extra inductance does nothing really as it can't supply any extra load on the negative half-cycles. You can solder those in parallel to the other caps using the through-hole leads on the back of the MB...

Other than that....(and this is sort of what I am designing as a Vcore booster except the whole regulation system with 4-phases and adjustable droop with be on a single add-on board):

Creativity: A+ :thumbsup:
Presentation: D-
Critical Flaws: F (caps)