I would say the reason why you don't read much about latency is because for the most part, it's a non issue. Most new or current systems can get down under 5ms with processing, if dialed in properly with good drivers.
My experience is, that spending the time learning the parameters of your given system, and how you can tweak it to perform for your needs, is the whole game. Unfortunately, unless you buy a system built with audio interface and software set up by someone else, you have to spend the hours, and days getting things just right.
My experience with the Digi002, MOTU, and M-Audio interfaces have all been similar with respect to latency, and their ability to monitor with processing, including high drain plugs like Guitar Rig.