Is there a specific delta-V for slingshot effect of a given planet/moon?

I'm pretty sure the orbital speed of the planet being used plays a major factor, which undoubtedly helped when Venus, (Mercury?). then Earth itself was used for (I believe) the Cassini probe to Saturn. The high speed of the planet being approached prolongs the time the craft is accelerating towards it. The notion that the velocity of the slingshot matters seems to be reenforced by what I've observed online in "My Solar System" I am pretty sure that there's a net acceleration relative to the world being used, because that world is decelerated just a little bit, freeing up laws of enegy conservation. Are there any sites that list the net delta-V of the various planets (or planet/moon combo),in the Solar system? By planet moon combo, Jupiter & its moon Io-it seems-could make a good double slingshot, combining Jupiter's massive gravity & Io's high "tow along" orbital velocity around Jupiter. Anyone know what the potential delta-V would be for Jupiter? I assume there are specifics somewhere in the equation, I'm not sure delta-V is that or not, but I don't see how it could be anything else. I assume there must be a maximum (net)delta-V for all worlds, although I'm sure the gravity well entry speed is a factor. The greater the initial speed entering the "G" well, the shorter the time accelerating because you pass through much quicker. But there must be an optimum dv potential.