N=8 SUGRA versus String Theory...

I was attending SERC(Science and Engineering Research Council) THEP (Theoretical High Energy Physics) Main school in IIT Guwahati from 2nd -21st March 2009. It was during a string theory tutorial when I asked this question to the tutor Nemani Suryanarayana (IMSc, Chennai). My doubt was like we remove the quadratic divergences in scalar field (Higgs) theory by introducing supersymmetry, is the same technique can prove useful in removing or controlling the divergences in the S-matrix theory of gravitation. Since getting a renormalizable (finite) theory of gravity is one of the main motivation to do string theory, I was wondering if that could be done with usual quantum field theory with supersymmetry. Prof Nemani told me that N=8 Supergravity (local supersymmetry) in four dimension may give rise to a finite theory of gravity, but nobody has proved it beyond two loops so far. Today however I have seen a paper which was put in ArXiv sometime in May(http://arxiv.org/abs/0905.2326) which discusses this issue upto four loop calculation. Although this is a good improvement over earlier results yet someone has to prove it for the most general order. Then only a finite quantum theory of gravity with N=8 local supersymmetry will be possible. Its difficult for me to comment on string theory since I hardly know much about it. Even if N=8 SUGRA comes out as a finite theory of gravity in four dimension that won't rule out or do any harm to string theory. They are not mutually exclusive, rather one converges to another asymptotically. It is also to be noted that N=8 SUSY is unrealistic, our world has N=1 SUSY (if any) and N=1 SUSY is not enough to remove the divergences which appear in quantizing gravity. Thus although a finite N=8 SUGRA in four dimensions will be a good news yet that's not the end of story.