I'm sure that iPhone 6 is s great device still but having got so used to 3D Touch I would find it hard to go "one level down".
For me it's an "s" or go home/wait.
Besides the 3D Touch ability you got the great deal stronger A9 chip; double the RAM (which makes a diff); better front & rear cam; 4K video; stronger 7000 series aluminum; Live Photos etc...tons of benefits
Eish wena...you have an obsession over 3D touch...sure it's a great feature but not the end of the world. Millions of people enjoyed their iPhones already for years, before this feature was introduced...
Anyway, to go to the 6 would be a level down for you perhaps, but not for the OP or his wife...
OP, the 6 in itself would still be a great phone - fast, takes good photos, etc. One really doesn't always has to have the latest and fastest and best specs...I mean, what features/camera quality/RAM/system chip will the 7 or 7S offer one day? But we don't have those specs yet - does that mean the phones we have now (6, 6S) are so bad that we can't do anything efficiently with them? No, of course not...but they will be considered "bad" or "slow" once the 7 and 7S are here one day. Funny how our minds work hey!
So often a lot of features and specs are wasted on people. OP, get the 6, nothing wrong with it, just keep in mind December is 8-9 months away, not 6 months. Vodacom is advertising great deals on the 6 now, "clearance sale" - I suppose the stock on the 6 is becoming less.