I know technically I should half hole the G to get G# but is it acceptable to do xxoxx? It sounds pretty close to G# on my Sindt in a fast tune. Any other suggestions for G# please?
The whistle is a very specific instrument meant to be played EXACTLY like it’s supposed to. By THE AUTHORITY!!
Under no circumstances must a G# be fingered other then half holing.
Also high D MUST have the top hole open.  Contrary to popular grumblings to the contrary.
There!
Ok. Just kidding. I haven’t had a lot of luck getting a G# with any fingering of my whistles except the Gen and Serpent. I’d do it however you want to. That’s my 2.5 cents.
I’m no authority… However, from my limited experience, some whistles will pass the bottom register G# xxo xxx all right, some not at all.
With my Kerry Pro Low D, it’s in tune, but a bit weak, just good for a passing note. With my Grinter Low D, it’s really all right, tone and volume wise. For some reason, this also has the best C-nat oxx ooo, but is there a connection?
With my high whistles, xxo xxx is unacceptable. If I badly need it, I grab an A whistle.
Here’s what I’ve found–your experiences may vary.
On narrow-bore whistles (Oak, Gen, Susato VSB, Clare, most inexpensive whistles), the lower octave G-sharp as ( x x o | x x x ) will be sharp to badly sharp and the tone will suffer, but usually on these same whistles a really good second-octave G-sharp can be had with ( x x o | x x o ), which can be very handy.
On wide-bore whistles (Susato, Cronnolly, Dixon, Serpent), a good first octave G-sharp can be gotten with (x x o | x x x) and a pretty good second octave G-sharp with ( x x o | x o x ) or ( x x o | x d o ) where the “d” signifies to half-hole.
On keyless flutes, half-holing seems to be the only way to get a good low octave G-sharp, and ( x x o | x d o ) best way to get the second-octave G-sharp.
Best,
–James