For this project I think it is fair to say that a 600mA supply is likely to be underrated and so a second opinion on the first advice was appropriate.
Fortunately, there are also some complex psychological effects that end up meaning that "perceived brightness" for a pulsed LED may have more to do with peak brightness rather than average brightness, at least under some circumstances...
I will not try to pose as an expert on human vision or “psychological effects” by any standards, but I think there is less to the above than meets the eye, literally so to speak. It is generally quoted that apparent brightness of a pulsed LED is more determined by peak actual brightness rather than average actual brightness. This is true under some circumstances, but mainly due to physics rather than human vision or “psychological effects”. Understanding why and what those circumstances are might help with LED based lighting designs.
A LED pulsed at 20mA with a 10% duty cycle will typically appear much brighter than the same LED with a steady DC of 2mA. The main reason for this however is physics, not psychology. A LED as a light emitter is simply less efficient at low currents and so a pulsed higher current will produce more brightness given the same average power.
There appears to be general consensus that human vision is non-linear and that a small increase in actual brightness will result in a relatively higher increase in perceived brightness. So far so good, but when it comes to time-integration, peak brightness plays a very small part whereas average brightness correlates well with perceived brightness. So for a multiplexed design, average power is the dominant perceived brightness factor as long as you keep the LED operating at or near peak efficiency.