If you can afford it, definetly do the jet training. But also do the light twin training. Do as much IFR training as you can. You get one chance at this ( well maybe two ), you need to bias everything in your favour. I'm not sure of the cost of the jet sim training, but if you get into qantas it will be well worth every dollar spent. Its also tax deductible if your employed in aviation.
I had about 10,000 hours flying when I went for my qantas sim test, and I still couldn't believe the pressure that you put yourself under when actually in the sim. You realise that everything depends on how you fly this sim. The outcome, your dream job, or another few years in the wilderness.
Above all, try to relax, know that you have done all you can in the way of preparation, and give it your best shot.
Good Luck