Robin Redbreast

I have a real #firstworldproblem - which superzoom lens to buy for my Olympus?  The best one technically is the 300mm prime BUT it's heavy and no flexibility in focal length; it is, though super sharp and has extra stabilisation built into the lens and the teleconverter will fit that too.  My worry is that it will be too heavy for me to handhold for any length of time. The other option is a Panasonic 100-400 - super-zoomy, much lighter but not f2.8 - it's also quite a lot cheaper (but I'm trying to leave that factor out of the equation}.

By way of 'experiment' I took my 40-150 + teleconverter out and searched for a few birds - this robin was quite obliging, as were a couple of ducks.  Handheld at full zoom these are sharp, but I do need a longer zoom if I am to achieve decent wildlife shots.  I might go to the lovely people at SRS in Watford and try out both lenses and/or borrow the Olympus for three days under their 'try before you buy' scheme.

It's a tough life.