Hi Keyes 1,
If you are buying new, why change brands.
What about an 8.0 m2 Sailworks Retro.
You already know how to rig and tune your 6.5 m2 Retro so an 8.0 m2 Retro would be very easy to transition up to.
You would need a 490 cm mast, but if you ever intend to go to bigger sails (and it sounds like you are ready now) you will need the longer mast.
Hope this helps,