Not whining, speaking from experience, the Britpart yellow or Deflex orange bushes are made of a far more brittle material with a much larger crystaline structure and a rough surface finish than SuperPro. This is the reason they fail so quickly, and SuperPro last longer.
If they get eaten with the suspension setup above, then they get eaten, but even if they cost 50% more I bet you will get more than 50% more life out of them compared to Britpart/Deflex bushes, meaning they are better value in the end.
With the SuperPro or equivalent, make sure you use plenty of the lube included with them, it makes a big difference.
The other option which should really be considered, is to re-engineer the suspension so that it doesn't destroy bushes every time you take it out, something like revolver shackles would reduce the stress on the bushes by a large amount, and don't have to be costly, they can be DIY if you want. Something like this, just a quick google for them:
http://www.difflock.com/buyersguide/newproducts/gone2far/Spring-Mount1.jpg
Chris, with anything like the above setup, or even just paras and 1-ton shackles you will end up having to notch the cross member too, moreso with the large amount of droop you seem to be being driven towards.
Rolling back a bit, is fabricating new shock mounts within your capabilitiess/design/comfort zone? Is it even something you want to do? Do you want to chop your cross member about to acheive max droop, or is it a lovely new galvanised one that you really can't bring youself to do it to....?
You've not really said much about specs or use other than 'mostly off-road', which can mean a lot of different things.... A bit more info I think is required before you spend £1K and another month trying to get it all to work together properly.