After considering the many options for an affordable telephoto lens for my OMD, I finally settled on the Olympus 40-150, for a couple of reasons.
First, the Oly is cheap. Well, not exactly here in Belgium, where it costs about 300€, which is hell of a lot if you ask me! But more on this later.
Then, according to what I've read, it has the best sharpness across the range compared to the Panasonic offerings. The 45-175 seems nice, but I've come across many negative reviews from people complaining about shutter shock. The 45-200 is said to be quite soft at the tele end.
Then, there is the 45-150, which again seems quite nice, but from a test I've read, the Oly is sharper.
Since I have IBIS on my OMD, I did not care about OIS. (even though it might be useful).
Ok, so paying 300€ for this lens was out of question. But I found a good deal on ebay, in a german Olympus shop selling many reconditioned items. And I found a nice EPL-3 with two lenses (14-42 and 45-150) for about 300€.
Fast forward a couple of days, camera received. Ok, it's almost new, with only ~600 actuations. Everything is as new. The kit lens looks nice in black. The 40-150 is very light!
After some testing, it seems like my copy is rather good, excellent across the frame from 40 to about 65, then slightly soft on the left side wide open from 70 to 110, and then again very good across the frame up to 150 included.
I think that's very fair for a cheap tele! I then compared it to my old 30D with 55-250, and there is no comparison. The Oly 45-150 is much sharper at all focal lengths.
As a side note, I quite enjoy the small 14-42. I bought my OMD body only and I used the P14, P25 and O45 until now, but I'd like a small zoom as walkaround for outside pics. The 14-42 is not stellar, but decent enough. I would like somewhat better sharpness wide open. The new Panasonic 14-42II seems very good in this aspect.
The EPL-3 is a nice little camera, also! Ok, the sensor is old, and not on par with the OMD at high iso, but up to 800 ISO, quality is excellent. The images are very comparable in jpeg to the OMD.
However, in my experience, the IBIS is close to useless. I used the EPM2 before, and this EPL3 somewhat behaves better (no shake induced by IBIS), but it's still hard to confirm that it does any good. Really, this seems like fake advertisement. When I was considering Olympus, I thought "hey great, I will have IS and fast primes at the same time". Well, only the OMD qualifies actually.
People are being deceived by this.
Back to the 40-150. A nice lens to be sure. Sharp, contrasty, lightweight. I don't really care for the plastic lens mount. It seems solid enough. IQ is really very good.
Here is a compulsory moon shot. Full tele, 150mm f/5.6. Tripod, 2 sec delay.
Nothing special, the lens is not long enough, but it's sharp.

And a rabbit

Not sure why, but I'm having a hard time getting perfect sharpness. Maybe it's shutter shock again. At 1/320 with IS on, it should be perfect. Here you can see slight blur. And it's not one picture in a series, but the whole series. At 1/1000, everything is tack sharp, and at 1/50 also. Strange...