I would suggest you go as cold as you have the ability to. I am brewing something similar using dusseldorf alt yeast. I think other yeasts you could consider would be the steam beer yeast or koelsch yeast. I think both benefit from cold aging after primary fermentation is done.
For my Oktoberfest Ale, I am going to push my system down to 64* and use the Dusseldorf Alt yeast with an oktoberfest grain bill.