I dug a little into the new w5200 files, and I was partly incorrect. The new w5100.cpp and w5100.h files will work with either the w5100 or w5200 depending on the define in w5100.h. If you comment out this line, it will compile for a w5100.
#define W5200
I tried to compile for a w5200 by adding that define to the sketch code, but it had no effect on the library code.
edit: Attached is the w5100.cpp and w5100.h files I am using. It has the 605 bug removed. and the w5200 define commented out.
w5100.h (14.5 KB)
w5100.cpp (5.36 KB)