Th basic racemic amphetamine consists of levo- and dextro-amphetamine. l-amphetamine is not considered as "fun" as d-amphetamine. 10 mg Adderall contains:

Dextro-amphetamine Saccharate- 2.5 mg;
Dextro-amphetamine Sulfate(USP)- 2.5 mg;
Racemic-amphetamine Aspartate- 2.5 mg;
Racemic-amphetamine Sulfate- 2.5 mg.

That's a total of 6.3 mg of the straight base amphetamine (excluding the salt weights). Dexedrine contains pure dextro-amphetamine and is considered more recreational by many.

Dextro-amphetamine dosages are about 2-3 times higher than that of meth, in my opinion. With little or no tolerance about 25 mg oral (equally to about 30 mg of Addrall) should give a decent buzz. But it doesn't last as long as meth due to the missing methyl-group which makes it easier for your body to break down the molecule. Common duration for amphetamine is about 6 hours.

You can't really compare dextro-amphetamine to street speed since you never know how pure or impure street-products are. You can't even be sure the stuff they sell you is meth or amphetamine rather than a substance like ephedrine or caffeine.