I strongly suspect 3.0 Amps on the +5 VSB rail is safety margin overkill and my DG45ID manages quite happily on a 350 Watt PSU with 'only' 2 Amps max on the +5 VSB. As this part of the supply is used to power devices that remain in use when the rest of the computer is off (eg parts of network cards for WOL functioning), it'll depend if you have lots of extra devices plugged or slotted into the board which may need powering in such circumstances. If you have no additional devices like this, I'd ask the supplier to test your preferred PSU with your board and make sure Wake On LAN works properly - if so, go right ahead. If there are others here with this board model, I too would be surprised if they are within that 3.0 Amp limit and would be even more suprised if using a 2.0 Amp max +5 VSB PSU results in issues affecting this type of functioning.
This is not the official response but it is based on my experience with another 4 series Intel board (in my case with an E8500 CPU).
Many thanks for the reply, I hadn't considered the possibilty of needing to power other external devices in standby so can see that would increase the load but, yes, it does seem like overkill to me too and it's encouraging to hear I'm not the only one who thinks so.
I've located a reasonably priced CIT 500W Micro ATX unit that meets all the other load requirements with a margin and allows 2.5 Amps on the standby supply so will probably go with that, and try not to think about what a 500W PSU in that small format is likely to do if the fan fails:-)
I had problems too meeting some of the other recommended limits with a 300W or even 400W Micro ATX PSU, the dual +12V loading for example, which is why I've decided to go with the 500W unit, although I'm pretty sure that's also going to be overkill for my application.