Hi Torger,
I have an Aptus 22 and have also spent (a lot) of time searching for a tablet which has firewire capability. I stumbled upon this, and it looks promising:
http://www.motioncomputing.com/us/products/rugged-tablets/j3600It's a tablet, has Win7 Pro, can be configured with an I7 cpu, up to 8 gigs memory, has an ExpressCard slot, and has TWO batteries which are hot-swappable... I haven't bought it, YET, but the specs seem to indicate that it could work well. Oh, and it weighs around 3 pounds, and you can get an option for gorilla glass and a high-end display screen...
The base model goes for around $1600 US, but that comes with an I5 and only 2 gigs memory, which likely isn't enough for Capture One if you are using it. Still, you can get a better cpu and memory and and and... It just costs more money.
My only real last question about it, is whether or not I can find an ExpressCard for firewire which does not need to be externally powered... Currently, I have one from Siig which I use with my laptop, but it does require that I also plug in and power it externally; the laptop won't do it on its own..
Hope that is helpful,
Foster