Olympus M.Zuiko Digital ED 40-150mm f/2.8 Pro is the best Micro Four Thirds zoom lens to date. Sharpness, contrast and resolution is outstanding wide open at the 40mm zoom setting, and very good at longer focal lengths too.

http://www.photographyblog.com/reviews/olympus_m_zuiko_digital_ed_40_150mm_f_2_8_pro_review/

http://www.seldomscenephotography.com/2015/02/16/the-olympus-40-150mm-f2-8-lens-for-butterfly-photography-a-user-experience-review/

http://www.fotozones.com/live/index.php/page/articles/_/misc/olympus-40-150mm-f28-lens-review-r140

https://www.flickr.com/photos/princecody/sets/72157647525749104

http://www.christography.com/blog/photographing-butterflies-with-the-olympus-40-150mm-f28

http://www.samudranil.in/blog/?id=123897549606#.VdP17k3vqUk

Olympus’ top end lenses, like the 75mm f/1.8 and all the PRO zooms, are known for their high level sharpness right from wide open. The 40-150mm PRO continues this trend and offers great sharpness from f/2.8 and at every focal length between 40mm and 150mm.

http://toolsandtoys.net/reviews/the-olympus-40-150mm-f2-8-pro-lens-review/

I picked up this and the 12-40 for shooting with my AF101 on corporate jobs, and for still shooting with the GH2, the 2 cover every situation and I get amazingly sharp images with nice colour rendition, a great investment. If I could also justify buying rest of the Voigtlander M43 range to join my 25mm I'd be a very happy man :)

Overview with samples

http://www.ixbt.com/digimage/olympus-ed-40-150mm-f28.shtml

https://dc.watch.impress.co.jp/docs/review/prolens/1086998.html

Sale

http://www.getolympus.com/us/en/outlet/outlet-featured.html