AGP 1.0 3.3v 1X 264MB/sec
AGP 1.0 3.3v 2X 528MB/sec
AGP 2.0 1.5v 4X 1.1GB/sec
AGP 3.0 0.8v 8X 2.1 GB/sec
AGP Pro is not a speed, nor a signal voltage. Instead, AGP Pro is simply an extended slot that adds power pins to both ends of the slot to facilitate certain graphics cards' (typically, those once used in professional design or A/V work) added power requirements. Because of its added pins, an AGP Pro card won't fit into a standard slot.
For the same reason, however, motherboards with a wider AGP Pro slot can accommodate a standard card. In this case, the added power pins of an AGP Pro slot go safely unused, and you can generally follow the above convention in figuring out compatibility.
For this reason, unless you're using an older professional graphics card, you don't need to worry about whether or not your board has an AGP Pro slot.
And frankly, you're not likely to be using a card that requires an AGP Pro slot. Gaming cards like the Radeon 9800 Pro (for example) are not AGP Pro cards, since they derive their power from separate power connectors. (In fact, that model has become the route taken by most professional cards today, which use the Molex connector of their gaming counterparts rather than an AGP Pro slot.)