Sped and speeded are both standard inflections of the verb to speed, and neither is more correct than the other. The old rule, purveyed in many English reference books, holds that speeded works only in the past-tense phrasal verb speeded up, but this recommendation is dated.

"Speeded" and "sped" are both correct inflections of the verb "to speed". They both represent its past tense and past participle form. One thing I would say, though, is that if you choose to use one in a text, use that same variant throughout for consistency.

speeded. Contexts . . Verb. Past tense for to move quickly. Past tense for to advance, or give a boost to. Past tense for to drive fast, especially beyond the legal speed limit. Adjective. Moving than a quicker than normal speed.