If cost if no option you should still get a 128gb msata for your OS. Let me tell you why.
If you have your OS and Work drive on the same disk your 512ssd, you run into the problem of bottleneck if you try to massive read and write on the same disk. With your OS on a msata you open up the bandwith for your work drive and cause non of your software and OS will ever need to run off the work drive.
This way you get 250mb r/w on your OS drive.
And 500mb r/w on your work drive.
So in the end you should buy both the 512 ssd, and a 128gb msata.
Thank you for for the post, but honestly, the mSATA interface is a greater bottleneck than just running everything on a 2.5" SSD. Also, if you're constantly pushing 250+MB/s on your drives, you don't need a laptop, you need a server with an attached SAN.
Yes, cost was not a limiting factor in the build of this laptop. That being said, I'm not going to spend money on something that most likely will offer no perceivable benefit.
The setup I have is plenty fast for what I need. *shrugs* This isn't my first computer configuration rodeo.