Apart from the curve, the only things different between HU8500 & HU7500 is that the former has PurColor and Auto Depth Enhancer. Auto Depth Enhancer is applied in curved screens only, so probably not that important. PurColor increases colour gamut. Only a side by side demo will show if there's any difference apart from the curve.
Although Currys prices are same as Richer Sounds, it only offers a 1 year warranty. Richer Sounds offers a 5-year warranty (so does John Lewis, and they both price match as well).
Besides, Richer Sounds and John Lewis consistently feature in top 5 in customer service, and there are many complaints about Currys customer services. I would recommend buying your TV from John Lewis or Richer Sounds for superior after sales support.