Ceiling height in old house - how low can you go?

We have a Victorian single fronted house being extended upstairs.

Currently downstairs has very high ceilings. Some, perhaps all, will need to be lowered to allow for second storey without going against heritage overlay.

How low could you go for a ceiling in a Victorian era house without it looking just plain wrong?

Basically it seems as if we can lower ceiling from second bedroom back and have four bedrooms total (two up, two down). Only one of the two upstairs would have access to an en suite. The other would have to walk downstairs to use bathroom. But ceilings would stay original height at front of house for a few metres at least. First impressions etc.

Or we can have the ceiling at lower height all the way through and have both bedrooms upstairs with ensuite.

What do people reckon? (Sorry I'm not clear right now on the eventual ceiling height with option two.)

Property is a rental house in West Melbourne. Tenants likely be an exec rental, young professionals share house or family who are renovating elsewhere.
Personally, I'd try to keep it consistent all the way through - and as high as you can get. But if they're 12-foot ceilings (which is reasonably standard for the era, I think), you might get away with 10-feet throughout.
We have a Cal bung with high ceilings in the original part and a 1980 lounge room extension at a more modern standard 2.4m or 2.6m (hmmm... not sure what that is in feet - 8?) and it's noticeable when you go from one to the other. In the five-year plan is a new living area and kitchen, and one of the must-haves for that will be a ceiling height to match the rest of the house.
It is more exe to build though. There are formulas for this stuff, so I'm not sure how to work it out. But obviously taller walls=more materials and some other highly technical equations.
my 2C only. I'm sure others will be begging to disagree. cheers.