Which VF?

1) If cost is no barrier, the VF4 is the right choice. Best resolution. Has a locking pin.
2) In the middle for cost is the VF2. Good resolution. No lock. Need to be careful it doesn't get knocked off.
3) Cheapest and smallest is the VF3. OK for framing and focus, but smallest screen, lacks "good" color, and lowest resolution. It does lock though.

Buy used/refurb. .

Editted to clarify the color comment on VF3. I have the VF2 and VF3,

 

The VF-3 has color. It is the lowest resolution viewfinder but works fine if you want to save a few bucks.

 

The em5 is 1.44 million.

VF3 is 922000 dots.

VF2 is 1,440,000 dots.

VF4 is 2.36 million dots.

All info is from the olympus website.

I would guess that the closest to the em5 viewfinder would be the VF2 or VF4.

 

The EM5 EVF is essentially the VF2. Most folks rave about the VF4. I know you want small, but you might want to consider it. It's most often compared to a good optical VF:

http://www.dpreview.com/reviews/olympus-pen-e-p5/4


Scroll down to the bottom of the page.

 

Used VF-2 are a good price now, and if you get the black one ... sometimes ... it looks small  

VF-4 always looks big, but optically it is superb.

VF-3 has its fans. Not me.

 

Also look on the Olympus website fro Refurbished specials.