I previously owned a set of STK S4 and currenylt own an Ilitch pickguard (same as his backplate) so heres my two cents:
The Classic Stack Plus is silent. Peiod. I have a ceiling fan, CRT, and a dimmer switch in my music room and the stacks were dead silent.
The Ilitch System does have some buzz, but it does knock down 80-90% of it. When I play it with high gain I need a noise gate, though the very lowest setting gets the job done
I have tried a lot of noiseless pickups: DMZ Areas, Fralin split Blades, Lace Sensors, Fender Vibtage Noiseless, and duncan. I can honestly say that the Classic Stacks are the best I have played. They really do sound land feeel like SSL1s (which I have also owned).
I personally prefer the spanky, funky sound of the Fender 69s to the fat, wooly SSL1 sound. That's why I currently use the backplate. Both options are great, it really depends on the tone you prefer.