Ok, yell if you've experienced this yourself:

Whenever the engine is under extreme load in upper RPM, it begins to cough and stumble. Power literally drops as if falling off a cliff.

It began shortly after I tuned my SU's and advanced the ignition from 10 init 32 adv. to 13 init 36 adv.

I don't believe its the carbs, as the car is running stronger than ever before (until X rpm, as stated below). I tested for detonation by putting the car in 3rd, and pulling as hard as possible up a hill from 1800 RPM. No pinging or knocking.

Just a complete lack of power at roughly 5500+ in 2nd, 4600 in 3rd, 4200 in 4th and 3500 in 5th.

Fouled or mis-gap'ed plugs? Point bounce? Fuel pressure a bit to low?

Fuel pressure... I'll check into that.

have you tried to back off the timing to 10 before TDC ? to much advance you will blow a hole in a piston if you are not careful. You are putting a hell of alot of strain on the pistons and rods . you will get by for a while but you are asking for trouble. that's my 2cts

Well, Steve Epperly (of ZTherapy) recommended I do as such, and like I said, I tried to get detonation by other means, but I never hear knocking or pinging.

First order of business is checking fuel pressure, then I'm going to dig into the distro and clean it out (weights and all).

Ok, problem solved... though not sure how.

Friend and I were looking at the distributor, then realized I was missing the wrenches necessary to work on it (its a bastard moving from domestic to classic import).

Figured we'd clean it out tomorrow. Put the cap back on and closed the hood.

On the drive home, car ran stronger than ever before. Revved clean to 7K. Took her to 145 to make certain it wouldn't fail under load. I'm not sure how the process of removing and reattaching a distributor cap can fix a problem, but I'm not complaining.

Wanted to thank you all for your suggestions though.