Options for Staying on in Oz - 857 vs 457 & LAFHA

Hi guys,

I did a search for this but couldn't find anything. I'm looking for some advice & opinions on what path may work best for us.

We're an unmarried couple, in mid 20s living in Regional Victoria, working as professionals in the same company and generally enjoying our jobs. Our social life is slowly picking up too which is always a bonus! Our Working Holiday visa ends in 5 weeks and it's basically crunch time for us to decide what visa to go for. We're looking at staying 2-4 years but this may change depending on circumstances. We have been guaranteed a job for 5-7 years assuming we don't completely stuff up (not economy dependent). We originally started working here to save for a deposit back home but it isn't 100% certain that we will make that move home.

The 2 options open to us are the 457 (temporary residency) or the 857 (permanent residency). Our company has said that they will reimburse us our necessary Visa expenses so the difference in visa cost isn't a concern currently (790 vs 2960).

First of all, about LAFHA:
Would it be seen as tax fraud if we both got seperate 457 visas and both claimed for LAFHA (obviously splitting the rent 50/50).

If we don't do this, we will receive $11,500 between us as "+ spouse" (just taking into account 1 income) as opposed to $9,750/annum each if we claimed individually. Or do we take into account our total income between the 2 and LAFHA do the sums on that? Surely we could technically be 2 friends who arrived in Australia at the same time and work in the same company? As long as we're not claiming double rent then there shouldn't be an issue should there?

The 857 however is looking tempting for us as it will give us Permanent residency which might be incredibly handy in 10 years if we've moved back to Ireland and discovered we've made a mistake or want a change of lifestyle.

We're pretty likely to stay here for a minimum of 2 years so can fill out the requirements for the 857 but is it worth missing out on a potential $19,500 each for those two years? If I knew we were going to be here at least 4 years then I would do a 457 for 3 years with LAFHA and then permanent residency for a year and then go for citizenship, but 4 years is a long time to make a call about now.

The other option of course is that we go for one 457 and one 857.....

Anybody else had the same concerns? Any direction, advice is greatly appreciated - I just want to make the right decision!

EDIT - Do we qualify for LAFHA as we have been working for this company on a WHV already?