I've had an M8 for a couple of years. It's fine, and a good alternative to the Studio Display. 5K would be nice, but it's not totally necessary unless you're really discerning. I didn't pay $700 for mine though - got it on a sale for $375. I could buy 3-4 of them for the price of a Studio Display, so for me it was worth it.
The OLED panel is probably nice, but at $1600 it's a bit too expensive. Once there are discounts on it, it probably won't be a bad deal.
The OLED panel is probably nice, but at $1600 it's a bit too expensive. Once there are discounts on it, it probably won't be a bad deal.