Maximum length supported by a LED RGB controller
Yes, your numbers sound correct to me.  Another way of looking at the standard 60-per-metre 5050's is that they are 3-channel LEDs, with 400ma per metre per channel.  (3528's are 1-channel LEDs, and the same applies; 400ma/metre assuming 60 LEDs per metre). 

I would not use drivers (power supplies) with a 10% derate unless I was using  top-tier suppliers (i.e. General Electric, Philips, etc.)   Most people use cheap Chinese power supplies off eBay/Amazon, and for those I recommend a 100-200% derate, i.e. buy 2-3x the power supply you intend to use. 



I don't know what your topology is going to be. Given the length and the season, my guess is this has something to do with Christmas lights on the interior or exterior of your house.  These tend to have a lot of linear run distance.  Let me talk about the challenges of carrying 12VDC a long distance. 

First, there's the internal wires which run down the length of every LED strip.  You can't use those.  They are quite small, and don't have the current capacity to daisy chain more than one additional strip - that's 10 metres tops - and at that, you'll still have serious voltage drop which will mean the farthest LEDs will be very noticeably dimmer than the near ones. 

There are two main ways to solve that problem. 

One is to run your own external "feeder" wire, and since you're RGB, you'll need to run 4 wires.  Then tie from your feeder to the strips everywhere you can - if possible, feed both ends.  The wire will have to be fairly thick - run it through a voltage drop calculator and you'll see. 

The second way is to avoid the voltage drop entirely by having several 120VAC/DC power supplies (drivers) distributed around the installation.  Each driver feeds only the LED strips closest to it, so 12V doesn't have to go very far.  How do you then control R/G/B mixing?  You use a device called an amplifier (aka data repeater).  It takes your controller's R/G/B output as a control signal at extremely low currents (easily handled by thermostat wire).  It pulses each channel same as the controller was, and sends that to the lights. 

A third option is to have a very fat 2-wire 12VDC feeder, and then several amplifiers distributed around as in the second option...
 so the 4-wire power only has to go a short distance. 

Cost would decide which way to go: copper (wire) vs. silicon (power supplies/drivers/amplifiers).