I think the major issue with Westwood's debut at Southampton was that he played three different positions in the space of 45 minutes and never had the chance to settle. When he had the opportunity to start and play one position for the whole game against Sunderland, he was excellent and deserves to stay in the team.
I'm with Percy. Some would argue Herd should be in there, but I'm not a fan, I'd have Delph in ahead of him if necessary. The four mentioned would naturally play quite narrow so I think you'd have to assume Gabby would have to be played as more of a wing forward than an out and out partner to Benteke to make it work though. A slump from Bannan or Ireland and Holman's straight in for me.