Go 7.1.4 - more is better! grin
Seriously though, I am far from a tech expert on this, but as an analogy, I have a small HT room and had a few comments when building that 5.1 would be enough for my space. But similar to your thinking, it'd be harder to go back and add 2 channels than just put them in up front. So, since I had the walls open and money set aside anyway, I went ahead with 7.1. and I will say it has helped me with the upgradeitis itch. Never say never though!

Cheers,

Dan
On-Wall M5HP LCR, QS8 & EP500 in 7.1