750Gb HDD plus 240Gb SSD Upgrade as Second Drive

Depending on the model series you could have encountered issues as the first optical drives were PATA which is a slower interface than SATA, It also had issues with booting when you put a converter and SATA SSD. Even the newer SATA optical drives didn't have the fastest interface as the interrupt level was lower than the HD's SATA port. These are the issues you likely read about.

As for the newest MBP model it still has an lower interrupt SATA port for the optical drive so it is slower. With that said I would recommend switching the drives around so the SSD was using the HD's SATA port if you go that route. The only risk here is the HD's anti-bounce logic is part of the logic board so you do run the risk of damaging your HD if you bang your system.

To be frank here, I don't recommend the dual drive setup in the newer MBP's as the current hybrid drives are a better solution. Seagate offers a nice unit.