Having ridden on a motorcycle into mountainous, rough terrain and also having had the "pleasure" of riding on similar roads with a multicab (which is the kind of 4 wheel drive vehicle you will likely be getting) I find there is a reason why they use motorcycles. The 4x4 you want to travel in will be very rough riding (shock absorbers? who needs 'em?) and very slow and unless you have a lot of luggage or a whole lot of people you will likely choose the habal habal on your second trip in :-)
I'm saying your wife will likely 'go along' with your choice but she would not consider the motorcycle method to be "roughing it". This is Philippines, its how things are done here and she surely knows that.