Hard Drive Questions: Which Configuration is better?

[rocknpop]

Hi guys,
Situation:
I have a MacBook Pro 9,1 (mid-2012, 15 inch; 2.6 GHz i7, 8GB RAM)
I have an internal 3G OWC SSD right now (max write read speeds of around 240 MBps), and an external OWC
I mainly use the laptop to record music with ProTools 12 (hence the need for fast read/write speeds)
I'd like to

1) increase the read/write speeds from ~240mbps to ~500mbps (planning on buying OWC's 6G SSD)
2) increase the hard drive memory with a fast read/write drive​

Hardware Considered
OWC 6G in the main drive
OWC 3G as a secondary drive

Possible Solutions
1) UBS 3.0: Use the USB 3.0 connection to connect to the 6G SSD, but I would prefer not to use the USB drive for an external drive.
2) SATA: Install 6G SSD in main drive, install 3G in optical SATA connection drive, however, the optical drive calls out a maximum negotiated speed of half the main drive (1.5GB vs. 3.0). If that is the case, the max speed I could get would be 130-145 MB/s using SATA?
3) FireWire 800: Same as #1, but FW800 instead on the connection

My hunch tells me the SATA connection is faster, but the negotiated speed is keeping me from doing this. Any advice would be appreciated.

 

[thats all folks]

negotiated is the speed of the device it's connected to. your current system drive is SATA 2 (3Gb) and your DVD burner is SATA 1 (1.5Gb). if you replace either with a SATA 3 device it will negotiate at 6Gb.

 

[rocknpop]

Does that mean that I can connect a 6G SSD to the optical drive and get the optimal speed (511 MB/s)? This is the drive: https://eshop.macsales.com/item/OWC/SSD7N6G480/