Ironing out the plumbing

We've started the basement plumbing, but now are starting to second guess what we've done. Since the floor is all ripped up, we have a lot of latitude with what we can do. We're thinking of getting rid of a large chunk of cast iron pipe, so we can move the toilet upstairs, and get the basement plumbing back to it's original level, since the house sank about 2" at the back, there is a flat section in the pipe. I wanted to keep the cast iron, because it's quiet, however, we'll never be ripping the basement floor up, so now is our chance to get everything right. We could do hubless cast iron for this small section in the basement, it's just so much harder to work with, and more expensive. I don't think the noise in the basement would bother me, and we could always insulate the pipe to lessen the noise. So we're leaning towards replacing the pipe. It would help with the layout of the laundry room as well. It's just a lot of work, and a major disruption.

We got another bin today, about 5 yards, so we'll be busy for the next few days filling it with dirt and concrete. We need to dig the basement out, so we have 3.5" of concrete with 4" of gravel under it. Currently the concrete is only 2" thick and it's right on the dirt. I'm surprised the whole floor isn't cracked.