Agreed if you already have a Fuzion then the upgrade to a Supreme probably wouldnt be worth it... Try the quad nozzle from the accelerator pack on the Fuzion for £4 - that should give you better temps than a stock Fuzion and Supreme
However my personal preference at the moment providing you have a decent pump with a high pressure head would be to go for the Supreme due to the fact you can actually get 1/2" hose on the barbs easily without wrestling with it for 30 mins
I'm with the rest of the crowd on this one... It's not justifiable to spend the extra money on a block that may or may not render noticeably better results in your setup. The D-Tek is a badass block anyhow, I'd stick with it!