You can't possibly be getting a better signal through optical, because Hawksford says it's mediocre.
Or you can go by 12 years of experience with ADAT and 15 years experience with SPdif optical and know that it's a very clean medium, as long as you don't exceed the length requirements.
You probably aren't going to get separate AC because the whole building is likely running from the same transformer and it all comes from the same grid. The key may be isolated grounds, at least in one case that I had, where I was getting interferrence from a large band saw when they'd operate it at the mill shop next door. Took 6 months to figure out that one. My building and their's, the breaker panels were grounded to the water pipes, I was getting interference coming through his water pipes, into the water main and up to my building via my water pipes. I bought a new breaker box and ran all of the gear to it, instead of grounding to the pipes, I sunk an 8 foot grounding rod outside and it immediately cured the bleed problem from the mill shop. I'm quite certain that it was a shared ground issue and if you are sharing the same ground as the other folks, than I would suspect that you'll get clicks when their ac and fridge compressors come on, maybe heater fans and microwave ovens which are notorius for introducing hum. Microwaves that use power up down settings to regulate heat are notorius for not only adding hum, but clicks when the power settings shift and an increase in hum level when they are on the higher setting.