Get the 870 Express that comes with the Factory tube ext. It is a better deal. It doesn't have mag tube dimples, comes with a extra power mag spring and has the detent ball on the barrel ring like the 870P. If you don't want the tube ext sale it for around $80 make about 1/3 your many back and replace it with a after market mag cap with sling swivel. Take advantage of the rebate before it ends on 12/31.
Express Model 5077 with tube ext is going for around $325, which has already been posted.
GC