1 5 Gbps vs 3 Gbpps

Different versions of SATA can be mixed - the connection runs at the speed of the lower rated component. Occasionally a particular brand of drive will have difficulty connecting to a particular motherboard chipset if the SATA protocol versions are different - in this case most drives have a jumper that forces them down to the next lower speed rating.

I have had SATA I and SATA II drives mixed without using jumpers and without any problems. I even had them running together in a RAID array.