Working from a external harddrive, but which one?!

I have been looking around for a while but there are so many people giving their opinion and i can't get a hold on it.

I got a Mac Book Pro Retina 15"

specs:

Processor; 2,3 GHz intel core i7

internal memory; 16 GB 1600 MHz DDR3

VideoCard; NVIDIA GeForce GT 650M 1024 MB

Harddrive; 251 GB SSD

I do some editting with Final cut pro X with 1080p HD files (H2.64 and prores) made with a Canon 7D, but I find my harddrive getting to full when working with big projects.

So my question is:

I wanna buy a external portable harddrive that is 1TB or higher and a USB 3.0.

But I would love it if it would be a 2.5 inch drive and bus powered (this means powered by the usb if i'm correct) so I could use it everywhere I go.

IS THIS POSSIBLE?

I'm going to use this drive to put the events and projects on that I would be editting at that moment. When I'm done with those projects it i would park it on my back up and erase it from the portable disk to keep the free space going.

I have readed about the 5400 rpm to be to low for editting from and most 2.5 inch external drives are that. But is it really that bad that you can't use it for that? And if you would, what kind of problems with show up?

And if it's that bad, is there a 2.5 Inch drive that is 7200 rpm with usb 3.0?

Note:

I would love to buy a Thunderbolt Drive but they are just to **** expensive.

Edit:
and yes I saw that there are several discussion goin on on this subject but most of them are out dated, so i created a new one