If the 5k is a hard limit, going by RRP you're looking at the Stumpy Comp 29 and Optic A9.1. SRAM GX drivetrain is practically identical. You've got Guide vs Level brakes and 150/135mm Rockshox vs 120/110mm Fox suspension.
I bought an Optic C9.2, and due to kids haven't had time to really dial it to tell you it slays everything. One thing I know is I don't really ride terrain that warrants the extra travel, so I decided to consider only bikes in the 120mm travel range assuming a better pedalling platform (which is not always the case). The other thing for me is I'm a Shimano shifter guy, and the Optic C9.2 was one of the only bikes at the time being specced with XT, a plus for me as it saves cost and hassle of replacing a new drivetrain.
If I was in your shoes I'd be considering what travel you want as it is the major difference between the two and since you're not in Perth you'll get a better chance at demoing both. One other thing - have you considered the Fuel EX 29? The '8' comes in under your budget, and the platform has been getting great reviews over the past 2 years, and fits in the middle with a symmetric 130mm front and rear travel spec. The '8' also runs a Shimano drivetrain if that is your thing.
If you're considering swapping around with 27.5+, then don't get the Optic. Rear clearance is much narrower than the Stumpy or Fuel that it looks like a wider tyre wouldn't fit. I haven't been able to test however I'd reckon it'll clear the top of the tyre ok, but the sides would rub.
If you need any specific info about the Optic I'm happy to answer.