I advice against getting a 4-8 spd IGH for your riding pattern. People tend to project all kinds of fantasy wishes into IGH's imagining them to be zero maintenance everlasting devices immune to wind and weather. IGH's have their uses, but they actually need maintenance just like any other mechanical device. The last official Shimano doc I have seen says that a Nexus 8 spd IGH needs an overhaul every 5000 km (3100 miles, but much lower intervals if used in bad weather), but someone well informed on IGH's on this forum says Shimano now recommends 1000 miles per overhaul, which is total in line what local mechanics in my country says. The 1000 miles rule is for all weather high mileage fast commuters, if you are a fair weather low mileage commuter the service interval can be much longer.

Overhauling a Nexus IGH isn't a trivial affair at all and probably isn't cost effective to do many places in the world, so now Shimano has a new procedure where you just simply dip the entire innards of the IGH in a special oil (70-100$ per 1 liter can).
IGH's need maintenance too, and if you don't, then the IGH will simply die. I know several people who wrecked their Nexus IGH's within a year or two and talked to dozens of people with the similar experiences. Eg. the bearing races on a 8 spd Nexus are easily pitted, but since the races are part of the hub shell that isn't sold as a spare part, this means buying an entirely new hub or rear wheel.

For all practical purposes Shimano IGH's are disposable items that aren't cost effective to repair; if the hub develops shifting problems you adjust cables or perhaps flush it in oil, if that doesn't cure it, you exchange the entire gear hub.

Here are some pictures of Nexus IGH's where road salt or water has entered the inside of the hub:
http://www.yellowjersey.org/photosfr...t/nx7brokn.jpg
http://www.yellowjersey.org/photosfr...t/alf8rust.jpg
http://www.astounding.org.uk/ian/hubgear/mangled.html

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Regards