wow uber cool as well!! congrats!
about the growth rate, i think its possible for either subspecies at 2", thats about 2.5" in 3 weeks. as a comparison, senegals that small can likely put on 1"-1.5" in that same time frame.
about the color, i've seen pics of them from a very shiny silver/platinum to white to kinda like the color of Li's fish. guess that just depends on the genes.
as for its ID, i can see how its head could look like a congicus, but at the same time an endli can definitely also look like that (actually i feel that at the same size congicus has a longer/narrower head compared to an endli. don't know if thats just me seeing things). i guess thats not saying much...sorry

anyway more updates as it grows would help. for now, the more i look at it, esp. the head, and compare to other endli/congicus pics, the more it feels like a P. endli. endli. to me, so yeah thats my answer
couple other things:
1. at 2", i'm guessing its farm bred? which country was it imported from? to be honest i'm not aware of any farm bred congicus.
2. although its not as obvious as a normal-colored fish, you can kinda see that 'dark' stripe on the upper part of the tail, thats a pattern of the endli. congicus tail don't have stripes like that.