All my heads come with Dual springs. Why? Because your motor is more than stock. If you are thinking of increasing the cam, compression or carburation, then you should consider better valve train components.

Cam:
The stock cam has low lift. Lets say you add an Engle #100 to your stock motor for more midrange and top end power, you have just added more lift and more duration. Now that added lift times some ratio rockers and your valves are opening a lot more than before, and faster. This makes it harder to control the valve train. What this means is you are asking more from your stock springs. You now want them to coil more and at a faster rate.
"Not a good idea"

Compression:
By adding more compression to your stock motor the cams characteristics change. This may extend the rpm higher than expected. Now that little motor can rev higher and faster and controlling the valve train is crucial.

Carburation:
If you increase the carb size, then you have just opened the window to RPM. Yes, now your motor will rev higher and faster. Although the stock carb is like a built-in rev limiter on most stock motors. With the larger carbs you can now feed a motor more efficiently at higher rpms. Its all about volume. This will change where the power band comes on. So if your motor makes most of its power from 2500 to 4000 and you add larger carbs, it will move the power band to say: 2500 to 5200. You will have to increase the valve train for this change.