I'm sure that he would rather start at Arsenal than compete for his position at United.The question for Arsenal fans is that even if Benzema was available do you think that you would even get him because of other clubs being interested as well?
If he was available I could see definitely United being interested and then there would perhaps be other big clubs as well. We know that United offer higher wages and Arsenal stick to a wage structure, in this modern day it's ultimately about money so even if he was available I don't think you'd get him easily. Unless it's just you and no other top club after him which won't be the case.