I too thought about the J'berg flights too, but for example on the 1/3/2008, when the first delay started (out of Sydney), the J'berg flight was late, but still arrived around 15:00. That is more than sufficent to turn a 744 around to depart at 18:05 on QF1.
The aircraft which operated my flight which left on 29/2/2008 came from the jetbase, as I passed it in the bus from the domestic terminal.
FYI the premium Y is going to be fitted to the aircraft operating QF1 first, not Pacific. QF1 is meant to be all premium Y by the start of April. I belive that -OJK was meant to be the first fitted and she should be in service. That being said -OJK was originaly meant to be the aircraft that operated QF1 out of SYD on 1/3/2008 but it ended up in the hands of -OJH.