5mg of Methadone? I'm sorry, but for someone with a tolerance, that's just not going to cut it. Safety first is a great policy, within reason. If OP can handle 45mg of Oxycodone and is seeking a buzz, 20mg is a more reasonable starting point.
Be sure to wait at least 3 hours before redosing if you're not where you want to be. Ideally, wait a little bit longer, as some people metabolize faster than others. While you are getting used to the subtle differences of Methadone when compared to other Opioids, be sure not to use any other CNS depressants. Common killers of recreational Methadone users are those who redose too early and those who use Benzodiazepines and/or alcohol with it.
No one's trying to tell you to be foolhardy or to push the envelope for no reason, it's just a fact that 5mg of Methadone is unlikely to get you what you're after, if what you're after is a recreational Opioid experience. Methadone is already at a disadvantage in terms of euphoria and enjoyment due to it's long onset of effect and duration. I happen to really like Methadone though as a recreational Opioid. Everybody is different. Be careful though OP, Methadone is definitely not to be trifled with.