firstly - it has been debated that 19-nor and 4-ad will compete for conversion enzymes. i'm not supporting either side - just suggesting a little research.
2nd - although most PH cycles only run for 6 weeks or less, there would probably not be any detriment to going 8. is it really beneficial? maybe somebody can weigh in who has run a PH cycle longer and let us know if the gains kept coming...naturally in these cases you'll want to PCT longer as your test is suppressed longer.