I would never mess with Tramadol recreationally if you already have an opiate tolerance. Reason being, the amount you would need to feel anything for most people (unless you're one of the 10% who metabolize the drug super efficiently) greatly increases the chances of having a seizure. The daily cutoff is 400mg of Tramadol, but keep in mind, this isn't assuming being taken as one dose. It assumes you're dosing throughout the day as you would if you were prescribed it. Taking 400mg of Tramadol at once has caused seizures in people, hell it's happened at 200mg at once.
Some people have taken over 1g of Tramadol at a time and been fine (really, really stupid IMO), and others have had grand mal seizures at 200mg doses. In my opinion, stay the fuck away from Tramadol unless you're using relatively small doses to stave off withdrawal from regular opiates. It's a totally sketchy drug that has bitten many people in the ass.