thanks for all your replies.
I am going to go with a Senco PC1010 and 18 and 23 air nailers.
I really wanted the convenience of the 18v systems but the price of them (£400 each with batteries/chargers) puts me off. Also quite wary, as went through the "new tech" of a Bostich and Paslode gas nailers, both of which were a PITO - getting gas that was fresh

I had been sharing a workshop and would borrow the other guys 23 pin when I needed it, and had my own 18 brad. But have just got rid of the gas nonsense, so was looking at options.
Seth - thanks for the info on the CO2. I looked at it last week and was very interested but I don't have a supplier close to me. I may look at it a bit later.
People seem happy with the Senco PC1010, so hopefully it will be an Ok compromise. The old compressor I used years back was a lump, and I'm too old to be carting it up Victorian terrace stairs nowadays, but the Senco PC1010 looks manageable.