In my opinion they're also the same species, but certainly can display different traits. Similar to the altifrons variants throughout Brazil.
The Rio Araguaia variant have much more solid red through the forehead, and could be considered thicker/bigger fish. The Rio Tapajos variant generally have a more orange head colouration, blending with gradient to a copper colour through the gillplate/operculum.
Honestly, if you've found a store that sells both variants, I'd be inclined to purchase from them. Most people will automatically label Orange Head species as Tapajos variants, as literature on the species and variants is scarce, and any online research (especially forum based) will return "That's a Tapajos Orange Head" to either variant.
Whilst both species are different, they're both gorgeous in their own seperate ways. I personally kept the Araguaia variant and found well kept specimens in appropriate water conditions showed absolutely amazing red colouration.
Not the best photo of the Araguaia variant on the left, but you get the idea. Doesn't help with the comparison that the Tapajos variant on the right is an amazing wild caught specimen, either. Just to clarify, these are not my fish, and not my photograph.