'cold-water' is a misnomer. when i think cold-water, i imagine a fast-flowing mountain stream, or an underground body of water (like where the proteus - or 'covjeca ribica' in the local Croatian which translates into 'human fishy' - is from).
m. opercularis is from sunny pools of water, albeit not totally tropical ones. meaning it likes a VARIATION in temperature. they are from the koreas and china and such. not from thailand like b. splendens.
its temp range is corresponding to that. while tropical bettas and gouramis like temps of 78-84, much like new world cichlids; m. opercularis can be kept in water from 61-80, a wide range as one would expect from a more temperate creature.
but it is noted ( http://www.seriouslyfish.com/species...s-opercularis/
) that it exhibits best coloration at temps of 70-75, which is taken with other anabantoids to be the temp they are healthiest at. for example, i have seen plenty of pics of betta rescues where an ugly brownish-grey betta was taken from a small petco cup at 73F and while acclimating to a heated tank at 78F (still in the bag, and thus still swimming in NH3) start darkening to show the gorgeous color pattern of a black orchid.
so one species likes temps of 70-75, the other likes temps of about 80-85...
additionally m. opercularis likes neutral water (ph 6-8) thats moderately hard to hard (5 degrees or more is cited).
m. ramirezi likes water as acidic and soft as possible (i know a guy who loves em in the NJAGC, and keeps his breeding tank at almost no hardness at all, and a ph of 5.6 if i remember correctly).