2.5 mg is a small amount. I don't think it'd do too much even for someone with no tolerance. I'd try 5-10mg and remember that methadone can take up to 2 hours to fully kick-in.
Whatever keeps both of yer oars in the water...^^^ Again, what??? Methadone is over twice as potent as oxy; I have stayed high on methadone for weeks straight, with a ridiculous tolerance, though the bad thing about 'dones is you have to constantly raise your dose for comparable effects(Let's just say I went from 30-40mg getting me where I needed to be, and was in triple digits after a matter of weeks.)