How about using the first patch with the slicing optimization and 
additionally enhancing GzipFile with the methods required to make it 
play nice as a raw stream to an io.BufferedReader object (readable(), 
writable(), readinto(), etc...).

This way we still get the 350% speed up and keep it fully backward 
compatible, and if someone needs the extra performance they can feed it 
into an io.BufferedReader object thus:

g = gzip.GzipFile(...)
r = io.BufferedReader(g)
for line in r:
    ...