Have not seen anything posted on this site to make me think the 1.3 is worth the additional money.
In truth 1.2/256 is probably the sweet spot given this is version #1
We don't really have any useful comparative benchmarks of real-world speed. However, there's a bunch of moaning on here about slow performance and I can report that my 1.3/512 eats anything I've thrown at it. I'm used to a maxed-out riMac so am surprised how well this little machine runs things. Obviously I don't have a lower model to compare it with though.