Where does the limit sit with a stock fuel pump before needing to step up to an electric one? Would assume it is a combination of capacity/power output and intended use? Any rules of thumb?

My rule of thumb would be......stock fuel pump, stock engine.

Intended use does affect what you can get away with, i.e. if you only potter around the streets with short blasts the stocker might be usable on a 150hp engine, take that same car down the long straight at a circuit or strip and you might starve it by the end. Some guys manage to run them in 12sec street cars but thats really pushing it I think. If you do replace it make sure your regulator is suitable and the replacement pump is actually an upgrade. The CB ones are ok I believe.
Also if you really need a bigger pump you probably need bigger lines as well. My 2c anyway

ok on 1916 , twin webbers stock fuel line.

run the 2110 in the dc with a stock pump (new)with dual 44's and it loves fuel and yet to run lean

Dunno why people are so scared of stock pumps.
Plenty of folks out there running IDAs and stock pumps.

Classic example is Glenn Rings 2180, pumping out 200ponies with 48IDAs on a stock pump for decades.

My old 2332 with IDA's made 141 rwhp with a stock pump. Neer noticed any prolems but I ended up converting to electric to clean up the installation