Indeed, QF127 seems often delayed, but you would usually make it. HKIA connections for pax and bags are very efficient and fast.

One problem you may encounter is if QR127 departure from SYD is expected to be delayed by 2 hours. Then the check-in desk would not accept to check through your bags. You will have to enter HK and recheck your bags with whatever airline you choose on GF.

Unless I am mistaken, EK does not fly to HEL. They would sell you a ticket to some European airport with a connection to HEL. But there are many other options with late evening or early morning departures that you could find on GF. Managing the checked bags might not be easy though if they are checked through.. The airline might not have the staff/time to find them and retag them, especially on a cheap Y ticket.
But last minute one-way tickets are not going to be cheap. Might be a good idea to stick with one airline on this one-stop one-way ticket HKG-HEL, even if a bit more expensive. For example, the KL combination tonight (departs 10:45pm) is priced at HKD10,406, then LH at 11:25 at HK18,203, then more expensive later on (early morning).

Good luck