Need Extender Recommendations

An extender by the very function of how it works, will diminish speeds. To what extent though is the point. 

A standard dual band extend will cut its throughput in roughly half. reason why is that the extender has to recieve and then retransmit. and it can't do both at once. 

A  triband extender will loose some speed but not nearly as much because it reserves a 5ghz band just for router--extender communication. This keeps your speed up. But it still takes a little bit of hit. 

I'd be at minimum looking at the tribands with your home size. its fairly large for a single level. 

If you're needing more than 1 extender, I'd actually be looking at moving to a true mesh system and not an extender mesh system.