My Win 8 setup is an upgrade over a stable and mature Win 7 Ultimate setup.
Runs and works just fine with no probs, as do all my installed progs.
The whole thing takes up approximately 42 GB.
By comparison, this setup (Win 7 Home Premium, 64-bit) came with so much shovel-ware
on it that it weighed in at just over 60 GB before I'd installed ANYTHING.