Again, I cant help with the corners as I dry mount, but another factor with conservation vs museum board is finish and cutting. My favourite boards happen to be cotton boards which is a pig as they cost more! It is just that I like the surface texture, their colour (you will find out just how many whites and off whites there are) and the way they cut. I would have no reservation from a conservation perspective using the conservation 100% alphacellulose boards. You may find it cheaper to buy board in bigger sheets and to cut it down, tho you normally need a trade account to buy it at decent prices (much cheaper than high st). You can further improve the conservation of your images by ensuring that board does not touch the image area. Therefore if you print with enough of a border to ensure that after the mounting corners aer hidden, you can leave a gap between the bevel edge and the image, so much the better. The only probelm I have found is tat differnt papers have different whiteness to the base which may or may not go well with teh white tone of your particular board. The white thing I find quite hard to get right, esp if I show the paper base. Some bases are very stark.
Tom