It pains me to say it as I'm really fond of the GWP breed as a whole, but I have also seen some aggressive and wholly uncontrollable wirehairs.
Care need to be taken and an examination of their lines before purchase. I suppose this goes for all breeds though.
i think it all depends how you look at a wire, and what you want it do for you if it's going to face a half alive pair of antlers, tusks or teeth thrashing at it, you will need something with a determined attitude to succeed.
on the other hand if you want a dog that will find a dead un in the long grass 75 yds from you, get a lab or something it's horses for courses
wires are truly demanding and ruthless in pursuit and will hold a wounded deer down or pull the final curtain down on a wounded fox after tracking it, you don't get that without some strength from the dog and it's make up has to be different from some other breeds, I wouldn't confuse that with vicious and uncontrollable my wire is a lovely lovely dog, fantastic at home, but doesn't take any prisoners.
my wire is with me work and play nearly seven days/ nights a week, for me he is bang on and he has proved himself beyond anything I could have wished, very strong, determined and as hard as nails plus, I would think very hard about getting a wire if you're not prepared, they will overrun you in an instant, if he gets the chance, not for the novice or part time working handler they command a lot of one to one and even more exercise.
it says for itself but as cadex stated, get some history on the lineage and attitude, they are hard going anyway at first for the first two years, get the training in them years you'll see a cracking tracking dog emerge the other end
good luck
choose wisely
atb
phil