You actually gained bandwidth. PCI-E 3.0 has double the bandwidth as PCI-E 2.0. So at x8 with PCI-E 3.0 you are the same as x16 PCI-E 2.0. Your 3rd card is actually on a faster slot now because x8 3.0 is the same as x16 2.0.
No. To give you a reference on how generations of PCI-E are, an 8x PCI 3.0 is the equivalent to a 16x PCI 2.0. A 4x PCI 3.0 is equivalent to an 8x PCI 2.0, so on and so forth. So no, you did not lose any bandwidth, you actually gained a substantial amount.