You can work on being away roughly half the time. 8 week/56 day roster, 26-30 days away.
For a mid range seniority S/O (on the -400) that might be something like:
London - 9 days away
12 days off
LA - 5 days away
8 days off
London - 9 days away
8 days off
LA - 5 days away
Or any combination of the above! As a minimum, you get half the days away off when you get back, i.e. 8 day London you get AT LEAST 4 days at home.
A330 guys do mainly 3/4/5 day trips around Asia and the odd LA at the moment. They do more frequent trips but spend roughly the same time away from home overall, but the advantage is the missus and the dog probably remember who you are!
And yes, 5 years is about the average time as S/O for those promoting at the moment. That might drop closer to 3 years if all the talked about promotion goes ahead.
Cheers