I will give a stern word of caution on converting foreign grading scales to US GPA, it does NOT give an accurate picture of your performance or preparation. In the UK, obtaining a first class (70%) is non-trivial and very unusual among physics majors IME. In my country (Spain), where a 1-10 scale is used, passing a core course like the quantums or advanced CM's (goldstein and landau) on the first attempt is the exception rather than the rule (at my school I have seen numerous grade billboards posted for exams where everyone failed), and grades very rarely exceed a 7/10 as well. My grades just barely translated into a 2.9-3.1 GPA according to online grade converters that also do official conversions for a fee, however talking to many of the grad students and having seen some of the coursework and quals, my preparation in the core subjects and math is noticeably stronger (likely due to the fact they have to fill their first year or more with non STEM electives, many never even took linear algebra which puts them at a disadvantage in QM). I simply applied with my transcripts as-is accompanied by an official translation and got into 4 great schools.
I have had exchange classmates from Germany at my undergrad school (and have met additional ones as an exchange student myself in the UK) and I would say their preparation was the same or much better, most schools in Germany seem to have a traditionally very rigorous physics programs, so to the OP: I would not concern yourself with what your grade is equivalent to in GPA and worry more about providing a convincing case as to why you want to go into research field X (your statement of purpose), getting relevant research experience if possible (but any experience is good), ref. letters as stated, and what is actually in your control right now: doing well on the standardized exams.