How much do the dealers ask for 18"?
In regard to the kumo tyres, I can't comment on a mk5 but I have a set on my mk2.
They're ok tyres for steady day to day driving but if you're giving it some you can really feel them struggling to cope
And in heavy rain, on the motorway especially, they aqua plane pretty bad and don't offer much in the way of confidence.
At the end of the day, the ones I have at least, aren't really performance tyres, and personally I would replace them
Heard good things about goodyear eagle f1's but a lot of people on here rate michelins too