[quote

I am well aware that tests have been carried out by game shots, in the field, claiming they shot steel through old English guns and noticed no difference from lead. [/quote]

Well I have met a few who, in the field, wouldn't notice a difference if there was no shot at all!

Seriously though, the main availability issue here (UK) seems to be for suitable non toxic ammunition (and particularly steel) compatible with 2 1/2" chambers. There are some advertised, but actually getting your hands on a box to try seems impossible. In theory, you can get 1000 to order, but no one I have found locally will sell you just a box to try. I do not want to buy 1000 of something that is 'no good' or on which the wads degrade with time quite quickly.
I have read very 'mixed' things about Eleys "Pro Eco Wads" .......... many not being at all impressed.