Just spoke with a mate of mine whos a bit of a lighting nerd, he reckons that CN Light make the bets kits, sold by a user called londoncolour on eBay. They're all 35W, he says if you want to go to 55W buy a generic 55W ballast kit, but it will drop the colour rating. He says a bulb that's rated at 6k at 35W will seem more like a 5k at 55W.
Im just about to purchase this kit:
https://www.ebay.co.uk/itm/CNLIGHT-H...lN4z32-VDwOTfA
With 6k bulbs and then this 55W ballast kit:
https://www.aliexpress.com/item/1-Pa...4d1d3c00ZQaVdp
They should look white and apparently he has run that same combination in daily use for a year with no issues.