I've now clocked past 30K on my 05 GT JTD, and need a new pair of tyres for the back.
I've got the 18" rims and at the moment it's got Michelin Pilot Sports on all corners at the mo, which have been on as long as I'v had the car (since 15k). Guessing that the fronts at least were replaced before I owned the car, as these have got a bit more on them.
I am in the same boat, the set on my GT have done 23K (owned since new) and they are not dead yet, I reckon I would get 25K out of a set of 4, but we are off round Europe in the summer and I need to replace them before then (otherwise they will be down on the tread wear indicators half way round).
I had a look around and the Goodyear and the Pirelli look ok, but as Rab88 said - the compound is a lot softer so the lifespan is shorter.
The Michelin's are 92Y rated, which is a heavy weight rating, and the other options in a 225/40 size from other manufacturers seemed not to have such a high rating, not sure if its needed though on a GT, maybe on something a bit heavier with more horses (than my JTD at least).
Its interesting Abyss's comment that the Goodyear are more noisy as well, that was something I was hoping I could improve on by going non michelin.
Let us know what you get? I don't need mine for a month or two so I am just trying to find a good price on the michlin at the moment.