Help: I love M43 but on the edge

I don't understand... nor do you it seems... what is preventing you from successfully shooting indoor with M43. I personally find it easier and have a better success rate than ever. Why, you might ask? Easy: I can now affordably shoot with a 17mm/1.8 (35mm equivalent), ...and the same could be said for any other Oly primes..., and you'd be hard pressed to find any top quality equivalent FF lenses with similar wide aperture for even close to the price you pay in M43. You want to shoot birds... try a FF 600mm lens for comfort, not to mention the effect on your bank account! I can shoot comfortably at ISO1600, and even 3200, so what's preventing me from shooting indoor... certainly not the equipment. I point, shoot, no flash... and get great pictures. I get great pictures outdoors, at night, hand held, too!

So ask yourself, what will FF possibly give you that will increase your success rate? Once you figured that out, then consider FF. Can you make "better" images with a FF camera? You certainly can, but you can also take nearly as good images with M43 in the same conditions. The only difference as far as IQ goes will be a little less noise, but overall, the images will be just as good at equal resolution. So what is good enough for what use? If all you do is print photo books, and post images on facebook, then FF is overkilled IMO. If the odd time you really really want less DoF than what M43 75mm/1.8 can give you... there are software solutions out there do to just that.

I personally think that you simply have a bout of bigger is better feaver for one, but if you want it, then get it, it's just gear.  When you get tired of it, you can switch back to M43.