First off, I'm pretty sure GPH's new 'value pack' isn't for sale anywhere yet. Maybe Korea if you can figure out how to order from them on their difficult-to-understand web site.
If the 'new firmware' has any enhancement, it just looks different-- it isn't actually improved in any substantial way. The pack-in items are not exactly deal-makers-- the 'pouch' is the old crummy case (any DS or PSP case really does the job better), the handstrap .. well, I don't see what it's good for at all except hanging off the unit, the headphones AFAIK no one's seen so no one can attest to their quality. As for the rechargable batteries, again, probably cheapo batteries. NO CHARGER is included and the GP2X cannot charge batteries. So you may as well just buy some good Duracell 2650mah batteries and a charger, they are sold together in a pack at many stores. Useful pack-ins would be a power brick and a TV out cable, but they aren't included. :rolleyes:
As for GP2X.co.uk's "power pack" with a unit tested for higher speeds, they don't always work at that speed and had to be scaled back significantly marketing-wise because of it. If you buy a normal unit from gp2x.co.uk you are guaranteed to get one that was tested not to work at a decent overclocked speed.
So, I'd consider the best option to just buy any old MK2 and the accessories you need (probably AC Adapter and/or TV out cable) from the US (gp2xstore or something along those lines) or German distributors (evildragon's store).
Auritribe: As far as the 'latest build of the unit'... I'm sure it's just an MK2 like any other.