While we don't like the cables so much because they look ugly and they miss a few features, technically they are very good and between them and the modular connectors they are both of high quality to match the rest of the unit. Antec has pulled through in that regard and instead of just going to Delta, telling it to build it a PSU and slapping an Antec badge on it; it's thought about the product as a whole.
The extra efficiency won't offset the extra cost, but £135 for the hardware you get in the black box isn't particularly bad value. Whether you go for this or the recently lower priced Cooler Master Ultimate UCP 900W will get you an excellent PSU either way – if we had reviewed the Cooler Master a week later at £146 and not £160+ it would have been recommended too. With regards to the Antec Signature 850W, the bottom line is that if you do want to splash out on a truly premium purchase, this is certainly one to keep high up on the short list.