Running Raid0 on MBP 2011
If you have to stripe data across both drives, then you'll be constantly limited by the SATA II bottleneck. 

You'd be much better off just buying a larger SSD for the hard drive slot, or installing two separate SSDs as separate drives.

At best, you might want to look at creating a Fusion drive between a larger mechanical in the Optical slot and an SSD in the HDD slot. (Or even two SSDs...?)