I've never been one for mixing & matching sails, stick to a brand, possibly a single model and all the debate about mast curves, different downhaul tensions, wind range etc... mostly go away. My recommendation would be to find an Ice of similar vintage to what you have with the 5.7 & hopefully in the size you are after. 0.7m between sails for blasting is fine, any of the 5.0 Ice sails were good units. I used North ice sails for years, from 4.5-5.7 and loved them, very good range. At 85-90 kegs they have punchy bottom end & manageable top end. Great bump & jump with good characteristics in the waves plus they last for ages.
I have recently swapped over to 2017 Blades, lighter feel in the hands than the Ice still with good bottom end but superb control at the top end. Might be what you are after and the 5.0 is a brilliant sail but my Blades are RDM only, might need to check that out if you chose to go that direction. Never used the Gator.
Only issue I see is a 5.0 on a 131L board. Given your weight, the moment the wind/chop gets up you'll most likely want to bung a small fin in to partner with the 5.0
(&/or see if you can borrow a sub 100-90L board, I'm sure there are plenty gathering dust somewhere in WA
)