Yuck!
I hate this combo. I used to do it ALL THE TIME, but I hate it now. Not only did it destroy my brain faster than I could even understand what was happening, but it's not even that great of a high either.
The amphetamine takes away almost all the love from the MDMA high.. it turns it into a much more self-centered and narcisisstic high where you're only really focused on what will make you feel better... that's a sharp contrast from the regular MDMA high where I run around telling people how much I love them while I give the dog a back massage lolol. Honestly you would probably be better off if you just took speed by itself.. the two drugs are OK by themselves, but I find they aren't so great mixed.
If you insist on taking speed though, keep the dose quite low. You're talking about amphetamine paste right? Well, there's no real way we could know how much that is... it could be anywhere from like 15%-80% pure... I'd take like 20mg probably, maybe 15. The less, the better IMO. Only way I'd do this combo again is if I had like 5mg of pure speed tops with my MDMA