I reckon in Scotland you'd be very hard pushed to get further than 1 hour from a half decent trail.
when's the day? west coast much much more midge infested in summer than the east
We spent new year in Achiltibuie last year - just lovely, a long way to drive (4-5 hours from Glasgow/Edinburgh) but if you were going to the states then it maybe doesn't sound that far. That area is simply stunning and it's pretty remote too - no trail centres though if that's what you need!!
For a honeymoon though maybe Skye is your best bet? it's perhaps not quite as remote as some other areas but there are lots of good hotels etc for a proper treat meal - even at the peak of summer you can find remoteness on skye - specially up by staffin way. If you were happy with mixed off road/road riding i'd say it was perfect
East coast you could do a lot worse than findhorn, (not the hippy commune but the village!) it's a bit London Ya's on sea, but it's pretty and romantic for a honeymoon. Lots of trails both man made and natural in Moray.