I think Wanderlei will win this just by being the better brawler and better at delivering punches crisply.
I think both now have deteriorated chins and the possibility of stoppage is very high , Leben has always relied on his heart but Bisping really did show his flaws as did Anderson counter punching works extremely well and staying behind a jab is also very effective against him.
I can see Wanderlei throwing alot of counter hooks and overhands against Leben as he comes lunging in.
The Gif above really does show how bad Leben is at striking and how a simple duck and counter can easily beat him.