I think 675 yards is still a par 5. I would have thought the 'line' should be 701 yards to be a par 6 and I base this on a par 3 is standardised at 250, a par 4 at 251-475 a par 5 'in excess off', if you call the 250-475 the interim shot -225 yards, so 475 + 225 is 700.
We have a 696 yarder and you can get it in 3 shots, mainly 3 woods though even I have hit a wedge 3rd shot from the 638 tee. I do not know of anyone on in two of the 696 tee, though its been done from the 660s.
Probably to be a good par 6, it needs something to challenge at 450 which if carried you can get on in 3 whilst a lay up defines it as a four shotter, it would be a rare bit of land but its possible you could get a good one.