I don't think the meanwell will do 89% efficiency. Maybe it reaches that at about 30-50% load and then slowly goes down towards 75-80%.
Yes, to get 408 watts out to devices, the power supply will take 458w from the mains socket if it really has 89% eff. at 400w, which i doubt.
I encourage you to double check datasheets and do actual measurements because the real world is much different that what says on datasheet - if it says that the boost driver has 95% doesn't mean it will actually have that much efficiency in real world (it may achieve that with particular Vin, particular Vout, a specific inductor etc)
The PSU can probably do 500w with no problems, but I'm not sure how long it would last at continuous 500 watts. Look in the datasheet how cramped everything is, with capacitors very close to heatsinks. At 500w output, even with 90% efficiency you have maybe 30-50w wasted as heat. The fan is a 23 cm one.. it's going to be noisy. Unless you hack the psu and put a 80-120mm on top of it to keep it cool (and noisy)
How much is this power supply? I see it's $240 at mouser. As long as you do the design using boost converters, maybe you can just go for a regular pc power supply and run everything from 12v... a very good 650w gold efficiency Seasonic power supply with semi-passive fan (only turns on at slow speed at around 200 watts) is only $99 :
http://www.newegg.com/Product/Product.aspx?Item=N82E16817151118 Personally, I would use a 48w power supply and use buck drivers, especially since you have those 39v leds. 70.2 watts at around 90% efficiency is 80 watts ... divided by 24v is about 3.3 amps... a lot of current for boost drivers.
Plenty of drivers that support 48v and you also save money by buying 10-20 chips of the same kind, with same (or similar) parts required for each one.