stupidbloke,
if you can afford to wait or afford the lens, i'd strongly suggest that you wait for a nikkor. a 3rd party lens will always be a 3rd party lens. i recently spoke to a friend who was using the tamron and now he's desperately trying to sell it off because the sharpness deteriorates as time goes by because the build of the lens is not made to take any form of abuse to it. which means that you cannot accidentally knock your lens to anything at all. if you're in the MRT and the lens is swinging around your shoulder, knocking some people and there and the lens will not give you any constant result anymore.
the reason why many prefer nikons including myself is not mainly because of the sharpness (though some is) but the reliabilty of a lens. that being said, tamrons lenses are not reliable because i owned one. after shooting a few events, i realised that not only the the lens is really soft at certain focusing range anymore, but also out of focus images.
when i got a nikkor, i never have any problems with anything. after that i never looked back.
this test will give you the results of the both lenses.
http://www.makofoto.cz/nikon/objektivy/Tamron_17_50/tamron_17_50.htm
are you serious that the tamron's sharpness is comparable to THE AF-S Nikkor 17-35 f/2.8 IF-ED? are you kidding me, i've seen the 17-35 been put to a test with some primes because there's nothing comes close to it in terms for zoom lens. the 17-35mm is the best zoom lens ever made, period.