How much power do you have to be making to go to a main stud over the regular bolt? Can anyone explain why studding is better?

The rule of thumb I've heard and used on my engine was around 500 HP. Its very application and tuneup dependant however. If the engine is detonating, it can hurt the bottom end at lower power levels and if everything is just right, higher power might be safe. Better safe than sorry though on the bottom end.

Studs put a higher clamp load on the bearing caps to help them stay put. They change the shape of the cap enough that line honing is needed when switching to studs.

I use studs on everything. Real cheap insurance.

Studs also engage all of the threads in the block, whatever the bolt hole depth is, while bolts are restricted to their length minus the cap height.

Make sure you chase the block threads with a bottom tap to be sure you have full threads all the way to the bottom.

The only thing you get with the studs is a better
clamping force. Also dont bottom the stud in the block
to tighten it down(so it doesnt back out), dont use
locktite to just hold it. What I like to do is drop
a ball bearing down each blind stud hole, double nut
the stud and tighten it in, loading the stud against
the ball bearing. JMO

How much horsepower do you think a SB with ARP main studs + H-Beam forged rods could handle ?!

Stock crankshaft and main caps.