^no.
A lot of people see, to have a misconception of what a "speedball" reall is. It's an intravenous combination of cocaine and heroin (classically), but can also be an IV combo of heroin and methamphetamine (or another stimulant). However, the Cocaine + Heroin combo is more ideal of people who favor opiates, as cocaine is such a short acting stimulant especially when injected.
When you shoot heroin and coke, the coke does not make the heroin more speedy. What happens is you get the intense rush from the cocaine (which pretty much overpowers the rush of the heroin), and as you come down, you sink to the high of the opiate. Combining stimulants that are long lasting (like meth and especially MDPV) will invade on the heroin's effects. IME, shooting MDPV and Oxymorphone together was just a waste as the PV completely negated the Opana's effects.
Basically, doing a downer along with an upper isn't really a speedball, it's what people seem to refer to as a pseudo-speedball. Sniffing some coke or some methylphenidate after doing a shot of heroin, and then shooting some more heroin after the methylphenidate Is basically just trying to even out your high so your not too tired, but not too alert. This is actually probably more dangerous than just injecting both at the same time (assuming your using a micron filter for the methylphenidate as Ritalin as some nasty binders), and calling it a day. The main reason that Speedballs are dangerous is because offten people end up overdosing due to using too much heroin/other opiate. If you're doing dope, sniffing Ritalin, then doing more dope, and continue using in this pattern, the dope is going to catch up with you first.