I’d we are talking about adding code to a large existing production code base then there’s no way I can see to get 5x, let alone 50x. My experience and the data I’ve seen is more like a 10-20% improvement. We see the volume of code increase more than that but a lot of is bug fixes only necessary because the initial commit wasn’t adequately tested and reviewed. So the net effect is less.

Now if you mean generating some one off script or playing around with a prototype in some area you don’t know then I can see more like 5-10x but these are typically not the bottleneck for shipping software.

I'm waist deep in hundred thousand line code bases.

Biggest problem there isn't delivering the code, it's coordinating. Old problems are new again.

When every developer can now deliver 10,000 line changes in an hour, you have to be very tactful about how people carve up the code base to work in it.