I have the same set up as you. In my experience there is a clear sonic gain with the N-60 stabilizer nut. The added mass seems to benefits the 'bottom end' of the sonic spectrum and makes the whole presentation somewhat more relaxed. This can be observed with both the 64s and 64fx arms. Sonically the B-60 base does the exact same thing, with the added convenience of VTA on the fly.
If anyone is interested, I have a spare N-60. It's a replica, but then again this is just a piece of machined stainless steel. No washer, but the same weight and same dimensions as the original. The only difference is that the original has a sticker with the model number.
