Int SSD or ext HD for scratch disk?

Hey,

Coming from a rMPB owner user FCP 7 among other apps:

I was under the impression that my internal SSD would be perfect for editing and I wouldn't need an external HD as a scratch disk.

However I need to purchase an external HD for space, and meanwhile I'm learning that using the internal SSD as a scratch disk will wear it out more quickly, and that despite its speed it's still better to use the SSD exclusively for apps and the system.

It is extremely fast while editing; rendering and so forth is MUCH faster than editing on my borrowed (thunderbolt->) FW800 5400rpm 500gb Lacie drive.

So among all these options are USB 3 and thunderbolt hard drives, and I get the impression that these would be the same speed even at 5400rpm than my internal SSD while giving the SSD some breathing room.

Then there is the problem that thunderbolt drives seem nasty, noisy, expensive, though I would certainly prefer thunderbolt. USB 3.0 ones seem cheaper, more options, as a result there's quieter ones built for mobility, and so forth.

There are so many informative posts here about WD My Passport and similar drives being excellent, but I don't want to go back to Firewire 800, despite the fact that my office computers have USB 2.0/FW800 from which I need to pick up footage.

So therefore I'd prefer a somewhat portable drive that can transfer ~60gb project folders in a reasonable time and it seems like USB 3.0 drives to 2.0 ports will be very slow, and unlike thunderbolt there are no FW 800 adapters haha.

So I am narrowing in towards:http://store.apple.com/us/product/H...p-hard-drive?fnode=5f&fs=m.tsConnections=usb3
or the most expensive, 7200 rpm, noisier, thunderbolt equivalent: http://store.apple.com/us/product/H...drive?fnode=5f&fs=m.tsConnections=thunderbolt
I'm a little behind on tech: previously I thought anything above 1TB would use raid 0 without telling the consumer, so does 3TB mean greater failure rate? In that case would continuing work on my SSD and a 0.5-1tb external be better (with a crappy 2 TB backup for time machine)?

Can anyone please advise brands or storage methods? I posted here because rMBP owners who do design or editing seem very common and I haven't seen many similar posts.

Thanks so much.

 

Thanks, that helps narrow down my search