What gun are you using? Are you using 5/16" shafts? If not, try this approach first if your mechanism wil accept them.
IMHO the Pelaj slip tip is far better value than the Riffe, considerably cheaper and fairly readily available.
The best tips arguably come from the US however, Steve Alexander has a brilliant tip as does Bill Kitto, Aimrite and Darryl Wong. All these guys make tips that use SS cable, which by the sounds of your application, would be better than the Spectra cord models.
If you are only paying $60-80 for a shaft, you are possibly buying relatively soft 316 stainless, which a half decent mac will turn into spaghetti, rather than 17-4PH spring stainless which is far more bend-resistant but very much more expensive.
Adrenaline Spearfishing sell alternatives to Riffes' 17-4PH shafts, the Riffes are reputed to be a little prone to bending though I haven't had any trouble with mine touch wood, good shafts are as dear as poison.
Bit of a learning curve with using slip tips effectively, nothing too serious, but hence why I suggested considering a thicker shaft first up, even 3/8" is extremely viable.
There is some good footage on youtube of the South Africans spearing macs with Rob Allen style shafts, have you used/considered the RA slip-tube design?
If you have moved to WA, the locals will know what works best .
Cheers.