I didn't expect it to be so low! I am starting a massive construction and was doing the pre-planning. So I stacked up dirt and 128 was the highest build point. And sea level is 64 so that limits building to 63 blocks? Woof. I will have to redesign one of my buildings as it won't fit.
I also found my Z maxed out at 420 to the south. That right? Seems a weird number given everything else in Minecraft seems to be powers of 2. I would have thought it would be 512 or 256.