I thought this was rather slow - am I right ?

I was churning out a single frame every three minutes on one project, and at that speed it was actually moving along nicely, considering what I had going on.

It might be slow. Then again, it might be blindingly fast. It really depends upon the render dimensions, number of lights in the scene, the presence of P6's dynamic hair, various render options and material settings, your CPU speed and system RAM, etc.

Your choice of codec shouldn't have any significant impact on total render time. Not even if you'd decided to use MSU Lossless, which is one of the slowest damned codecs I've ever tested.