Hi Lude,
I think that post #4 here will give you some better sources for your latex.
Talalay has the edge over Dunlop in terms of breathability but bear in mind that the sleeping microclimate and temperature regulation is affected by the foam, the quilting and ticking materials (a good cover is a necessity), your choice of mattress protector, and the sheets you use so the foam is just one piece of the ventilation and coolness puzzle.
Bear in mind too that it may be less expensive to buy a mattress with the components that you are considering (either a 6" core or two 3" layers) with a good quality cover (which you will need anyway) than to put all the pieces together on your own and it may also give you more flexibility if you need to do any exchanges.
Other than that … my comments in the previous post will hopefully be helpful as well.
Phoenix