Actually, larger thinbars are alot rarer in the U.S. than the pulchers. Large thinbars might push a higher price in the U.S.
As for growth rate, I bought a silver dat about four months ago at 4", and now he is pushing around 8-9 inches. Thats a silver dat. I bought around the same time a thinbar, about the same size, and right now the thinbar is only about 5-6 inches. The silver dat eats alot, and pretty much anything and everything, sometimes I see it eat pellets, while the thinbar only eats krill and the occasional raw shrimp. I never see it with a full stomach, while the silver is always fat. The Indo that I have is about 10" when I bought it about 3 months ago, and looks to be the same size still, and it is a big eater also. The widebars (pulcher) I have four. Two I bought at the same time around 4inches, same time being about 4 months ago, and they are about 6-8 inches. The 10" I bought about 4 months ago, still looks like 10" but is much rounder, fatter, than I got it. When I got that 10", the color was dark, almost black, but now it is bright yellow, it seems to be from thailand, not vietnam. The 12" I bought about 2 months ago, still looks like 12 inches. They eat alot, except the thinbar. I am selling them, but I need to get at least the same price that I paid for them, or they can stay with me
I bought a 2" Indo about 3 months ago, and now it is 4".
I guess the growth rate depends on the size of tank you have them in, how much food you feed them, and how often you feed them. They are also sensitive to water quality, so a periodic water change is good for them. I trained my pulchers to eat beefheart. They love it, but the thinbar wont touch it. Hope this helps.