Pros and cons to JBOD setup on MacBook Pro with two internal SSDs

I've got an original Apple-installed 120GB 3G (3Gb/s) SSD which I'll be moving into the optical bay using an OWC "Data Doubler" and swapping a new 240GB OWC Mercury Electra 6G (6Gb/s) SSD into the main drive bay.

My goal is to avoid having two separate volumes.

Understand that a RAID 0 array would essentially only perform as well as the slowest drive in the array (the 3G SSD in this case), if it would even work at all given the two drives are not identical in make and capacity.

I've read that a JBOD array isn't subject to the "same make and capacity" constraints. But how does this setup perform?

Would the speed of the 6G be hobbled, slowed down to the 3G's speed (or worse?), if I were to set up the two SSDs as a JBOD array?

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MacBook Pro (17-inch, Early 2011, Macbook8,3) | 2.3 GHz Intel Core i7 | Yosemite 10.10.2