Intergrale 8 - What appeals to me most about the Kalkhoff is the Gates carbon drive. I have one (along with a Rohloff hub) on another non-ebike, and the low maintenance, ability to ride in snow/rain, etc. is a big plus. I really like my Stromer, so it is no knock on that bike.
I test rode the Stromer ST2 and it was fine - not enough to make me want to upgrade, however.