There is little to choose between them if you look at the Photozone tests
Pany
Panasonic Lumix G Vario 45-200mm f/4-5.6 OIS - Review / Test Report - Analysis
Oly
Olympus Digital Zuiko 40-150mm f/4-5.6 ED Review / Test Report - Analysis

At 100mm the Oly has the edge

As a respective owner makes no sense to swap one for the other unless you have a bad copy (which is possible) or not perfectly centred

For an Oly user the 40-150 + adaptor makes more sense while considering it costs less, you will have less reach and no OIS (Which has the edge over IBIS)

For a Pany Oly user (myself) the 45-200 is the better choice

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Catch that Light
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http://boyzo.smugmug.com/

Hi,

just to let you know that I posted a short series of 45-200mm pictures from a daytrip to the zoo here :

A short series from Antwerp Zoo

C U,
Rafael