Okay, well, here's my progress so far for any readers in future:
The main constraint of finding a suitable stand for this monitor was obviously it's weight. The size wasn't really an issue as long as the stand could hold the weight and keep it held, along with maintaining the ability to 'freely' move the display around on all axis.
Firstly I went to good old Amazon to see if Duronic had anything suitable (gass or spring based) with atleast 2 arms, as I've used them before on other monitors at work and at home with great success. For the price you can't really get anything better, solid build quality. But unfortunatley, their best 2 section gass arm topped out at 8KG, along with all the others... they had fixed pole variants that coud support upto 10KG's, but they were not what I was looking for in this instance. Although the U3415W is only .4KG over the rated spec on the gass arm, I'd rather not risk the fate of a £650 monitor in the hands of something that is not rated to work at that weight.
My next port of call was Ergotech Freedom Arm HD, something in which was highly rated by Hardware Canucks. It looked great, solid and for the price, reasonable. The problem was getting it into the UK. They were out of stock on the UK/EU store at the time and the US store did not allow for imports into the UK. So much for that idea then...
Next, to search on Amazon.Honed in the search criteria a bit more vigorously this time and came across something interesting in which took me a bit by surprise. The Dell MSA14. First thing I noticed was the price, £65, which is odd as Dell usually over charge heavily for this stuff (granted, on Dell's website, they sell them for an RRP of £84~), plus it was through Dell's official store on Amazon - right place, right time. After further research, it was perfect for what I needed. It was rated to support upto 9.3KG - check, fit well with the monitors design and actually looks nice - check, integrates well with the monitor (has the Dell quick release plate on the VESA mount) - check (nice feature) and last but not least - some really nice inbuilt cable management, check. I also looked around to see if I could find anyone else using that combo, turns out Dell themselves were using it at the reveal event of the U3415W to showcase it.
So, I picked one up and I shall do a follow up with my findings.