It depends a bit on your level and on exactly which boards you're looking at. But at that weight, no doubt a 65 liter board will be a more all round wave sailing board and when you're that light even most small wave boards will handle a 5.6 OK with the right fin.
But if you focus more on the less epic but more common days with maybe onshore and not so much wind and if you're not yet a super competent wave rider, than the bigger board could be the best choice. You will struggle a bit more with smaller sails, but that might be worth it.
The best thing would be to test the boards of course.