New efficient speakers - best way to keep noise floor down?

My speakers are 101db, why do you think about noise floor problem ?
Did you get the speakers or it is just in theory ?

It depends on your cartridge and cables, also the amp and phono stage.
I can’t remember any noise problem with my 101db (Zu Audio Druid) speakers unless it’s a cartridge with extremely low output (lower than 0.15 mV). All MM/MI are dead quiet on the home listening volume level.

I would recommend AT-ML150 OCC with Beryllium Cantilever and MicroLine stylus tip if you want the best for the bucks. Or the AT-ML170 if you want one of the best MM ever. Here is the article for you about some decent MM. Australian JLTi made amazing phono stage for MM/MC for very reasonable price, previous version without new PSU was exactly $750 new. 

I worry about the noise floor problem because in my demo the bg noise was noticeable (but still sounded bloody fantastic). However, even though their analog equipment was totally different than mine, I think they are of similar quality so I'm thinking I might need to plan ahead.

What is the rest of your system. The way the noise floor gets reduced is equipment with equipment that has low internal noise levels. A quiet phono stage is a good start, but you also want a preamp and amp with low noise levels.

Agree with Chakster. There are too many variables. I have Devore O93's and tube gear every step of the way to the loudspeakers and I used to have a hum problem with my VPI table due to a grounding issue. My other deck, a hot-rodded TD124 with a Reed 3P had zero hum. I believe my hum problem had to do with VPI's inferior and sometimes problematic grounding scheme with their junction box. Reed (and several other great arm designs) incorporates a cartridge clips to RCA continuous wire (no breaks along the way). My belief is that this reduces the chances of hum greatly. Shielded IC's from the phono stage to the preamp and from the preamp to the amp also help. In my case, I run balanced-Cardas Clear Beyond-from my preamp to amp. So I got rid of my VPI Prime and replaced it with a hot-rodded Garrard 301 with another Reed 3P and though both decks sport low output MC cartridges, my system is dead quiet on most days. Sometimes when the power lines are noisy, I hear very slight hissing. 

What may affect noise floor? The gain of the preamp and amp with regard to sensitivity of the speakers. It can reveal noise in the upstream components. May not be a problem with the right cartridge choice.

And of course, the amount of noise on the AC line coming into your house. Has this ever been noticeable before, and do you use any power conditioning?