Not sure why you smoke everything at 275 but we all have our techniques. As for how does the SI compare to a Cookshack, very well indeed in material and construction. I would say dead even. The SI "D" controller is a PID, and therefore very accurate and user customizable whereas the CS controllers while very good are not in the same league as a PID (that is NOT a condemnation of what CS uses). My SI 3D when it reaches my set temperature locks it in and there it stays with no drop or rise for the duration of the cook.
On my CS, I could watch the temp drop or rise a degree throughout the cook. I was good with that.
The racks in the SI are stainless steel rather than nickel plated as with the CS (stainless is extra). The racks on the SI 3D are larger than those on even the CS Amerique and will take full packer briskets straight in, as well as full lengths of ribs. Wheels are larger, the cord is longer, and of course there is the value. I firmly believe that dollar for dollar, you cannot beat the SI line of smokers.
I have nothing but good things to say about the CS 066 I used for years (and hoping my son enjoys it as much as I did). But I do prefer the SI 3D over the Amerique for a variety of reasons, chiefly the depth of the cooker. So convenient to put food in 'as is' without having to cut it to fit. Given a choice today as a first time buyer, I would go with the SI 3D and never look back.