No, you cannot get the full speed of PCI from each slot. PCI operates at a maximum speed of 266 MBps at 66 MHz or 133 MBps at 33 MHz. This enclosure features a PCI Express (PCIe) x1 slot (v. 1.0) that operates at 250 MBps.
The available bandwidth from the PCIe bus is split equally between the PCI slots, regardless of whether or not a card is inserted into each slot. The PCIe bus provides speeds up to 62.5 MB/sec per slot. This speed is sufficient for many PCI cards, but may impact the performance of higher-speed cards (for example, USB 3.0 PCI cards).