I've got a 6 week old 13" MBP with the 256GB SSD that came with it.
I've also got a 256GB SSD Intel 520 Series that I've been considering adding to my configuration lately.
In other words, all it'll cost you is $90 for your 16GB RAM & around $50 for either your OWC or your OptiBay data doubler...if you swap with me.
Are you really not happy with the 13 rMBP so far? I was so darn frustrated when I saw that the 13" version had come out, not 2 weeks after my return period ended!
Of course one of the things I like the best about the rMBP is the dual Thunderbolt slots, b/c I've had a crazy time trying to get the 13" MBP to run dual monitors, along with the laptop screen itself, whenever I'm in the office. Apparently it's a Mountain Lion/Displaylink driver issue, so it'll eventually get resolved, but it's still some kind of frustrating!
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Did you get one of those $10 HDD caddy's from Amazon yourself, by any chance?
I saw those on there the other day & was tempted to get one, I mean at $10 why not anyway I guess, but then I read some reviews where people were complaining that they weren't even getting the same caddy that was shown in the picture & it wasn't fitting anywhere near the way some of the other reviewers were saying. Like I said, I guess at that price it's worth it to find out though, I wasn't sure how they compared to the OWC or the OptiBay versions.