I'm trying to order a Walther LGU Varmint .177, but noticed it comes in two different configurations. One is the 11.8 fpe, and the other is listed at 17 fpe on the Krale site. Using their airgun calculator, the fps on the 11.8 fpe is 787 fps. The 17 fpe model shows 967 fps. I assume they're using some arbitrary standard pellet weight to figure fpe. I'm all confused now. Which model is the one usually sold in the US, and what would be the reason to get the lower powered model?