Hi,
As mentioned Maris Otter is a variety of pale malt and completely interchangeable, if the colour is different, that will be down to the maltster (level of modification and kilning temp) more than anything else.
The perceived increase in biscuit taste is very much down to the clever marketing of the licence holder of the grain performing the biscuit test, (made some biscuits from halcyon, pipkin or the like and Maris Otter), many years ago.
Any variation in extract (in litre degrees/kg) or flavour is mostly batch related than anything else.
Varieties come and go, as new breeds are introduced and farmers adopt them due to their harvesting times and yield. Imagine all of your barley ripening at the same time and you need to harvest it all in at once. All new varieties of malting barley are subject to brewing trials using EBC methods before it is approved for Brewing by the IBG (institute of Brewing and Distilling).
WBR
Hoppy