Help: 4x10 Cab/Head vs. 115Combo w/ Extension

I need everyones help on a decision for christmas. I currently have a Peavey TNT115, and i love it but I feel there is better out there for me. Im wondering do yall think it is better to upgrade to a nice head, and a 4x10 cab, or I heard just adding a 2x10 extension to a peavey TNT115 works great. Will I lose bottom going with a 4x10, cuz I want people to feel my B string. What do yall think.. ...Please Help!

I play gospel in an average sized church, any thing other than that would be small gigs. Thanks