Worldrunner, I think your workout program sounds fine. You're not a beginner so six weeks is probably a reasonable amount of time to be changing programs. As you become more fit your body adapts faster You are making progress (increasing weight) and body change will follow, it's just going to be slower than it used to be. If at the end of six weeks you are still making progress, increasing weight, reps etc it's fine to continue the same program. On the other hand if you are wrapping out sooner it's also okay to change programs faster, but probably not sooner than four weeks.(sources: Burn the fat, Feed the Muscle and The New Rules of Lifting.) When I say this, I’m really referring to the program itself, i.e the exercises. Rep ranges are a different thing. The biggest gains I ever made were a few years ago when I changed rep ranges every week and plenty of workout programs change them more often. Which I guess you know since talked about pyramids. I hear pyramids are awesome. I've never tried them personally. If you do do them I would love to hear how it works for you.
One thing I would change is you have your upper body routines on consecutive days. As Jim implied when you work the larger muscle groups like chest and back you are also working the smaller ones like biceps and triceps. Swap legs day with chest and back or put the strength days on days 1,3 and 6. If you want to keep them in a cluster I think it would be better to do front body (chest, biceps) and the back body (back, triceps.) Muscles are built when you are resting them. Exercise is the architect, rest is the builder.
As I said, it sounds like you're doing fine. If you're not already taking measurements it's a great way to track progress. The measuring tape will tell you there's a quarter inch difference that you might not be able to see with the naked eye. You can also compare your body fat percentage and weight each week to see if you are gaining or losing lean mass to give you a better indicator of whether what you are doing is making the changes you want to make. Every body is different and responds differently which is probably why you are getting different answers. It all works, but how well is it working for you?
For example, I have heard, anecdotally only, that some people who are having hard time gaining muscles have had better luck in the higher rep ranges 12-15. Something to keep in back of your mind if you are still unsatisfied.