I think it depends on what type of brewing you will be doing (traditional all grain, BIAB, extract). i decided to step up to the Polar Ware 40 quart because i want to do be able to do 6 gallon BIAB batches and liked the quality and dimensions of the Polar Ware 361BP. I was considering a larger...
42 degrees is a little on the cold side but after 6 days at 71 the fermentation may be pretty far along. I would rack it to the 5 gallon pull a gravity sample and stick it in the fridge. Monitor the activity and temp for a week or 2 and take another sample. If the gravity drops then let it...
What's you gravity at now? Are you racking to the 5 gallon so it will fit in the fridge? Or will the 6.5 gallon fit? I guess either way I would stick it in the fridge for about 2 months at the 42 degrees