im 180cm tall and walk around at 74-75kg I cut down to 70kg for my fights which I dont lose any cardio or strength, I recon I could get down to 68kg but I would not do it all at once, never drop more than 5kg on the weigh in day, these UFC guys that cut 10 plus kgs to fight have proper medical teams to help hydrate back up via UV drips ect, even with that if you watch the guys that do the big cuts they usually suffer if the fight goes past the second round, I would suggest you stick to your weight routine and go up a weight class, you will find you will do much better in the 70kg division if you got your walk around weight similar to mine, im usually a tad bigger than the guys I fight as I weigh in at 70kg but the next night I walk into the cage at around 73-74kg, plus its a good mental advantage to know your bigger and stronger than the guy your fighting,