I've said this MANY times on this board..... it's the LONG draw from the tank that is the most limiting factor, especially through stock 3/8" (or smaller) fuel lines. Like ALL fuel pumps, mechanical pumps push fuel better than they suck it.
A stock fuel pump could easily support over 500HP IF THERE WAS NO RESTRICTION ON THE DRAW SIDE. In some cases I've found the stock fuel lines poop out as slow as the high 13s, regardless of how big a mechanical pump I put on the engine.
What to do?
The single biggest improvement I've found to an otherwise stock fuel system is to add a low pressure electric "helper" pump back near the tank. I started off using the Carter 5 PSI "street pump" which works just fine but is noisy. I've since switched to the Holley Red which not only moves more fuel but does so with less noise. They don't draw much current either- 5A is plenty if you use adequate sized wire to power it (I use 10-12 Ga. wire for the long run from the fuse block). I always use a relay system, but in a pinch I've powered it straight off the IGN terminal on the fuse block and it works just fine.
The difference can be dramatic. The above mentioned combo that was running out of fuel in the high 13s was capable of running high 11s on nitrous with NO drop-off in fuel pressure and NO changes to the fuel system other than the extra electric helper pump mounted back near the tank (still using stock fuel lines and in-tank pickup).
Alternatively, you could rip out all the stock stuff back to the tank and replace it with 1/2" line. I grew tired of doing that since it costs nearly as much when you add it all up and it's a lot more work than patching in an electric pump. Plus you can get the car home on either pump by itself if the other one dies.
I've used this combo many many times in the real world. It's worked for me over and over and over.
1990 454SS pickup. Original "tow truck motor" 454 upgraded to something a little more "aggressive." Seems pretty stout but the fuel bill is nuts.
78 Malibu. Inherited with only 35K on the odo! Mild 383 with Weiand 142 blower on top. Mid 12s appears to be the best it's gonna do on street rubber. Runs so good I may never drive it again.
"Last remaining QJet tuner on planet Earth!"