I could use no flash, and the optics I have has a low aperture. I take photos that are almost black and then filter them afterwards. It sucks qualitywise, but it's the best I could do.
Y i noticed your pics with flash are much better and clearer, i know a photographer who always makes his pics darker in raw format, but i get your point, you could not use flash all the time.
btw those lenses are expensive as hell, u can get a whole computer for one nikon lens 1.4ED
Rothaarig3
100 less grainy as 10000
i used to make NO auto sharpness adjustments on my old nikon (SLR) F55