Photoshop CS6 gives the attached warning, which apparently doesn't apply for TIFFs, if one makes a file with e.g. 70000 pixels length, which saves just fine as a TIFF. Don't know if there even is a maximum as long as the total file size stays below 4 GB.
Cheers,
Bart
When that article was written, CS4 was around, don’t honestly recall what error would pop. But the size limit existed for both. Either way, going back to post #2, there’s nothing useful in .PSD sans Duotone support and as Schewe points out, best to stick with TIFF unless you hit thise size limitations