I haven't read Devereaux either, but I have heard plenty of rubbish talked about pyramids. If you want to build a tall structure without reinforcement or mortar, then a conical shape of some description is the only stable structure there is. The steeper the angle the less material (and hence work) you need to build it, but there comes a point where too steep an angle results in an unstable structure. There is thus a small range of angles that are optimal. Various pyramids in Egypt illustrate the stages of evolution of the ideal angle; the most famous being the "bent" pyramid.

The Egyptians had a way of measuring angles by taking the distance to the slope from a vertical cubit rod. This "sekhed" measure was counted in "fingers", a cubit being 28 fingers. The angle of the Great Pyramid is 22 sekheds, which means it has a slope of 22/28, which is the same as 22/(7*4) or PI/4. Many people have declared this to be remarkable, but it arises solely from the fact that the Egyptians tended to pick a whole number of sekheds and needed a value somewhere in the 21-24 range for the optimal angle. It's quite conceivable that the Egyptians knew about PI and that 22/7 was a good approximation, but it's unlikely that they intentionally built it into their pyramid since they built plenty of others that did not use this particular angle.

The angle of the GP happens to be around 52 degrees, which is similar to the latitude of Silbury. Big deal! It's also the number of weeks in a year and the number of cards in a deck. Are we to attach significance to those?

Coincidence is normal; it occurs with frequent regularity. There has to be much more than just a few flimsy similarities before a real link can be established.