If I understand it corectly, the specs which change are related to the hashrate.
The Rockerbox ASICs Spondoolies received probably have fewer functional cores than designed, which led Spondoolies to increase the clockspeed and voltage in order to get closer to the hashrate goal. This decreases the efficiency. The SP30s will probably still be limited by the PSUs after they are reconfigured in a factory-default overclocked configuration, but will have a lower hashrate. So, yes.
The issue I'm seeing here is only to overcome temperature limitations in the various setups. So if we power the units 220-240V, from Emerson you get 1200W per power supply, while Murata can give you 1300W per power supply. Hoping that the units can use all the "juice" they get, a Murata powered equipment will give you more "juice" to draw on. If the hashing boards are the same (which will not be the case) .. one would expect better output from a Murata powered unit.
1200W or 1300W is what the PSUs are rated for. However, Spondoolies tested each extensively, and believes that both models can be used well above their rating. They expect 1375W available from each model if you're using 200V-240V. I have seen nothing about what they expect on 110V-120V. If I had to guess, I'd say around 1200W.
In Canada you pay customs tax when you get them. Not sure how they'll calculate it in this case, versus a SP10, I guess by value

In US you pay customs tax if they feel like it (if it exceeds a certain amount .. your carrier knows better). VAT is Value Added Tax and you pay it in US when you go to any store and buy hardware, how much, depends on the state you're in.
USA isn't Canada. If you are trying to carry something into the USA across the border yourself, you may be hit with a 3% customs tax if the value exceeds some threshold regardless of the goods type. For computer equipment imported through some shipping method, you pay the specific rate for importing computer hardware, which is 0% (
http://www.dutycalculator.com/dc/109091-import-duty-rate-for-computer-hardware-is-0/).