Keep 3 things in mind when going with "pully sets":
1. Your power steering system only causes as much resistance as it needs to move the fluid.
2. Your alternator only causes as much resistance as it needs to charge your car.
3. It may be unnecessary for your water pump to spin as fast as it does at high rpms, but it needs to be spinning as fast as it does at low rpms.
That said, the only gain you are looking at getting, aside from attempting to undercut your charging system (the regulator will force the alternator to try and charge more, increasing resistance and straining your alternator) or deprive your power steering system (this system will also just demand whatever power it need regardless of underdrive) is through the water pump; the acessory that uses the most power. Just get yourself an electric water pump, and save the strain on the alternator and cooling system.
You alternator will not mind the 7 amp load from the electric water pump, so whatever tiny increased load the alternator sees will never equal the mechanical force necessary to spin that water pump at high rpms, and your impeller will be spinning much faster at idle than it ever did on the mechanical setup. Cooling system is happy, alternator is happy, and so are the rest of your accessories.
Trust me, as I have been through this on 3 different cars. The electric water pump delivered the best gains with the least amount of trouble, and the underdrives caused nothing but trouble.