Saull is in a different league right now. The guy has been absolutely immense for Saracens and one of the primary reasons why they're in with a chance of winning the league this season. The guy is lightweight I admit but as HRH Richard Hill (AKA God, the King of Kings and the best there was, the best there is and the best there'll ever be) has said, his technique, speed and attacking skill more than makes up that.
Look at Richie McCaw, what makes him so special? It isn't just what he does at the breakdown its the all round package that he brings to the All Black table. Its the fact that McCaw is just as comfortable in attack as he is ferreting through a dogpile sniffing for the ball that makes him special and Andy Saull in my mind reflects those same qualities.
Thats why Saull should get tapped for the Senior squad in place of Croft. Lawes in at 6, Haskell in at 8 and Saull on the bench waiting for Moody to run into a rugby post or something.
Edit: seriously, if a trio of Lawes, Haskell and Saull can't get the job done we may as well just throw out lot in with Brussels and demand an EU team.