Hi,
The example design document says the following:
The channel runs @ 150 Mbps after reprogramming the clock to 150 Mhz. This 150 Mbps is achieved using 11x oversampling (both on the transmit and receive side), the transceiver itself is configured at 1650 Mbps.
Oversampling has to be at both Tx and Rx side. Tx side you will be sending at the rate much higher than required and at Rx also you will have multiple samples of the same data, hence, oversampling.
For your case XCVR will run at 1250 Mbps only but at the Rx side you need to discard extra samples received.
Hope that clarifies.
Regards