Any reason to acquire more watts than really needed?
Are you sure every led is 60 mA? Or you mean maybe each Red, green and blue led inside each led (3 x 20 mA).

You always should buy slightly more than you need (but you think about 200W instead of 135W) already which is more than enough safety overhead.

Why would you need more? If you mean to control it with an Arduino Uno, that MCU (including the LEDs etc) is high likely more than a few hundred mA. So the only reason why you need more, is if you want to control later more LED strips, or any motor or other power hungry external devices.