Assuming that I have one router in one floor and 2 re-purposed routers (AP) in one floor each, how would I ensure that the devices are picking the correct AP/router that has the highest speed at that location.
Roaming beween APs is a device dependent feature
It's the network stack on the client device that determines when a signal level is too low for it to seek other available SSIDs -
that threshold may be set at a threshold of -80db or a SnR of 20db but unfortunately, for the most part, is not user editable
With a multi-AP setup, you will need to do a fair amount of hit & trial with the Tx power setting to find the right balance
Bear in mind that with multi APs, less is often better
Set it too high and your end user device may end up seeing high dB levels for the far away AP even when you are close to another AP
Set it too low and you will end up with dark spots between the APs
Also, don't put three APs where two will suffice (same holds good for a mesh network)
Too many APs will only increase the noise floor , esp on the 2.4ghz band
One more thing - and this is mostly anecdotal and based on my personal experience
Most routers except the mid to high end (and very new) models have poor 5ghz radios and tend to drop you to 2.4 band unless you are in very close proximity
I have seen significantly improved 5ghz range with the RBK50 compared to my nighhawk R7000.
Having said that, I have also heard good feedback on the 5ghz range on the newer R7000P from a close colleague
Worth noting though that 2 X R7000P will end up costing more than a RBK50