Turbochargers cause pressure between the turbo & the cylinder on the inlet & the exhaust. In an average setup the ratio of pressure on the exhaust side vs pressure on the inlet side can be as bad as 2:1. This means when you have 10psi of boost on the inlet you have 20psi in the exhaust manifold, any time you have overlap you have exhaust pushing up the inlet & diluting the incoming fresh charge, so any overlap is bad. With supercharging, overlap is a good thing, the right amount will blow the combustion chamber clean, too much won't hurt power but will hurt fuel economy.

Inlet valve springs need to have more seat pressure in both instances simply because the pressure is trying to hold the valve open. A 44mm inlet Valve has roughly 2.3 square inches of area, so at 10 psi you need an extra 23 pounds of spring pressure to counter it. The exhaust situation is worse with turbos because there is even more pressure, this isn't a factor with a supercharged engine. A good turbo cam for a B20 needs to be very short on duration so you could have very wide lobe centres to avoid overlap. Such a cam would have to open & close as fast as mechanically possible otherwise it would become a restriction itself. This type of cam profile then needs even more pressure. For a quality turbo install on a B20, a roller cam & roller rockers would be pretty much mandatory. With a supercharger the cam can be something which is more like a cam for an NA motor.

You are correct with valve sizes, with both force fed engines you would spend as much as possible on the exhaust side of the head but more so with turbo as it helps more in getting the pressure ratio down.

Cheers,
Paul.