404 Jeffery.

I've just put in my CZ550 in 375H&H to my favourite gunsmith, and am having it rebarrelled to 404 Jeffery. I had a look at all the calibres already mentioned by you all, and gradually discounted them one by one.

The Taylor and Hoffman in 416 were discounted due to no factory ammunition available, although the Hoffman had some appeal;

The 416 Remington was discounted due to higher chamber pressures than others;

The 416 Rigby, although a lovely low pressure, fine performing calibre, was a bit "brisk" in the recoil department, certainly sharper than the 458WM, and so was rejected.

That left the 404 Jeffery, which could be easily made from my CZ and should be reasonably pleasant to shoot, given all reports. Norma makes ammunition, and components are readily available. Plus, it has a fine reputation.