What do you intend to use the chains for? Traction aid for the mostly empty hobby truck, so you do not get stuck on the road on the way home? Then one set of ladder-type chains (e.g. miltary surplus), single-wheel type, is likely sufficient. Put them onto the rearmost outer wheels. No need to wrestle with dual chains. Alternatively, you can put them onto the front axle, 6x6 engaged, and the front wheels will pull you nicely around turns.
Planning to do off-roading in the snow, do heavy pulling/recovery with your winch? Get a set for each axle - duals for the rear and singles on the front. If you can, avoid the ladder type chains and go for the "criss-cross" type chains that also have extra chain links welded at a 90 degree angle on the short traction chains to increase the profile and to really dig in. Here is what I mean:
http://tirechains.com/TND-Tire-Chains.htm
They make you as close to unstoppable as it gets. They are also decent on ice, where the ladder-type chains can cause your rear end opening to hold the seat cover in a death grip. If you REALLY want to know what first-rate tire chains look like, go there:
http://pewagchain.com/
As for speed...having chains on when on bare pavement is illegal in most places. If the going is good, I'd restrict myself to about 30mph/50 km/h on packed snow with chains on.