Which of these PSU's would best fit my system?

Try getting one of these, the cheapest i could find online in down under...

for 750W
Corsair TX-750 - A$147
SeaSonic S12D 750W - A$168

for 600-650W
SeaSonic S12II 620W - A$143
Corsair TX-650 - A$115

I would also recommend this if you need something lower
OCZ ModXStream Pro 700W for A$ 109

Will the tx-650 be able to run 2 GTX 460's?

I thought it only had 2 6 pins?

Two GTX 460 in sli will consume roughly 425 watts under 100% load... that should leave you enough to run other components but its tight... i only looked for 650 since you had also quoted a couple of 650's... i would recommend 750W but corsair and seasonic always give extra headroom for loads and future component upgrades... so should be OK...

TX range is certified SLI ready - http://www.corsair.com/products/tx/default.aspx

It's got the power.
You are correct.
The oem platform in the TP 650 is basically an updated, enhanced and modularized version of the one used in the Corsair 650, it's a better power supply ( and has 4 pcie connectors ) for not much more money.