RT-AC66U or RT-AC68U ?

Hi,

The agony. Got an RT-N66U at the moment and slowly upgrading my wireless clients to be AC compatible.

Is there a need? No.
Do I want AC? YES.

Already got a decent Synology NAS, so USB 3 has no impact in my decision.
I do need Dual WAN (got an LTE USB modem backup).

I also prefer RMerlins version.

Are there any good reasons to go for RT-AC68U apart from bragging rights?
Anything I might have missed?

Pricing here in Oz is RT-AC66U about $230 RT-AC68U about $300.

Cheers