I've tried the stock, the LM4562 and opa627 board. I noticed more of a difference with the 627 than the other two. It may seem to be a smidge brighter but I think it is because of the improved clarity. Its also smoother. The LM4562 is a little warmer but perhaps a little more edgy in the treble. Both are an improvement over stock.
Pinch of salt required because the differences are very subtle.