A few days ago I purchased a dewalt 54v chainsaw kit (DCM575X1 GB) from FFX for over a £100 less than I could find it anywhere else. That same night I went looking for spare chain(s) and realised its an Oregon chain 90PX056, However different sellers are listing these with no suffix, an E or X (i.e. 90PX056X) and the Oregon website itself only lists 90PX056G.
I asked their customer service what the last suffix meant (as that seems to influence the prices from c £13 to £22) ....it just denotes the packaging used; the chain is the same in all of them. The same applies for any Oregon chain.
Dave