Summicron lens result on GXR?
Your question is under defined : 28/35/40/50/75/90mm ? and many variants.
Summicron only really defines a Leica lens with f/2 max aperture.
That said, unlike many APS and m43 cameras, the GXR, with it's sensor micro lenses, works flawlessly with pretty much any M lens in existence; the 28 and 90mm APSH Summicrons I have are no exception.