You have a real prusa!? That is awesome. I need to sell one of my knock offs and buy his, I really like his design and all he has contributed to 3D printing.
The longer the z-axis hangs the longer the moment arm. Is decreases rigidity linearly, twice the length half the rigidity.
I have not made the through table legs yet, I found that I never print anything taller than about 3.5″ so I built a 4.5″ Z and one with 4″ Z. Build to what you need. Try the legs through the table it should work out really well. 4 screws to adjust the height, Bet you won’t use 10″ very often but if you need it it will be there.