200k-300k boost from Tier 2 launch plus 50k-80k higher weekly average thanks to game launches like Destiny. Not to mention MK8 is running out of gas so Xbox One would outsell it even without those things. It's not the boldest prediction i know, but it might wake some people up who apparently think Wii-U will keep second place for long.

So how big do you guys think the difference will be?

this will be fun... i think it will be between +20k and -10k

Too much. I'm expecting to outsell the WiiU by 200-250K.

Not sure if serious! Imo it could outsell WiiU by about 200k. 

I expect to outsell by 250K for September, while 100K for October.

Nove and Dec the Wii U will outsell the Xbox One by about 400-500 K.....

since last year's 1.6m for those two months will practically double. The monthly sales totals are intriguing.

Well that is a way to forget Leo-j crazy predictions;..

Just for the month or lifetime?

Don't forget:
Fatal Frame and Bayonetta 2 come to Japan in September.
Hyrule Warriors comes to NA and Europe in September as well.
I think Disney Infinity comes to Wii U in September too -- that has more system selling power for Ninty than you might think!

I hate to say it but I think all of these games are largely going to flop. 

Hyrule Warriors might do "ok" in North America (ok in the "DKC: TF first month" sense). 

Mario Kart 8 is running out of gas? X'D Yes, it's definitely tapering off, I'm expecting it to stop selling very soon indeed.