New boiler for larger house

[AliHeat]

I am looking for a new nat gas boiler for a large (wood frame) house, 6 beds, 3 baths, about 5000sqft. I have calculated the heat loss at somewhere in the range of 40-60KW. (Yes, huge). It currently has an ancient, smelly, noisy, inefficient 85KW oil burner, but much insulation and double glazing has been installed since that was put in, and there is now mains gas available. It would also be used to heat a swimming pool in the summer using a heat exchanger.

So I'm looking at various offerings in the 55-65KW region: Keston C55, Ideal IMAX W60, Vaillant ecoTEC 65, Clyde CG060, Potterton Paramount 2/60, Buderus 800/60 etc.

Anyone have any useful advice about the choice from those listed above (things like extras required that affect overall costs, comparative installation costs, reliability, comaprisons between stainless steel and aluminium HX etc)- and have I missed any others I shoud be considering?

I'd appreciate any suggestions, advice and comments.