Fingering is the same on all whistles. However, depending on which keys you play, they will not play the same. For example, all six holes covered on a D whistle will play a D, and all six holes covered on a C whistle will play a C. And, all six holes covered on a G will play…a G. 
The high G and F Generations, in my opinion, are the best of the Generations made today. They’re virtually unchanged from the G and F Generations that were made pre-1980’s, except they don’t have the ridge along the top of the mouthpiece beak.
You can just fill under the windway with a little poster putty, and that sweetens and cleans up the G and F Generations nicely. The only other tweaking they might benefit from is to scrape a bevel onto the windway floor exit, but even if you just fill under the windway and don’t bother with the bevel, they turn out well. Clean, birdlike sound. Very nice whistles, IMO.
BTW, G Generation whistleheads can be removed easily, but F Generation whistleheads (like their C’s) are very difficult to remove without cracking.
Best wishes,
Jerry
Thank you both for your advice–I’ll keep it in mind. I yet to decide if it needs any tweaking, though–I haven’t played around with it enough, since I have some trepidations about disturbing my family and dogs in the area. 
Hi homelesshobbit—This page is a part of this website that you can also get to by scrolling down the Main Page—the place where you first come on before you click on Chiff and Fipple Message Board. It might help explain a little more about whistles and keys.
THis might help