So I tested 1 meter of the LED strips on the brightest white with the silly controller they came with and the whole set pulled 1.2A, 14W. So that's only 400mA per colour, I think the green pulled 420mA the rest 390mA.
So rather than running 2x1meter strips with the option of going to 4x1meter strips from one set of transistors, I could always create a little array of small transistors. For 4 strips it would be 12 transistors, but each would only need to handle 500mA.
As a bonus I could control each strip individually. Although that would require 12 PWM channels, which I would need to check. As it's for a fish tank I don't need much in the way of control, but I do need a way to shift the colour a little bit, probably dropping the green light a bit to favour the plants preferred spectrum, or favouring the blue to make the tank look prettier. Then again fading out rather than cutting hard would be better for the fish too, which requires PWM on all colour channels.
Without 12 PWM pins I could of course just run 2 transistors in parallel off one PWM pin to run 2 strings of LEDs from 3 PWM pins and 6 transistors. Meaning I only need 6 PWM pins which I think is available.