On the sharpness of the 100-300 @ 300mm

It must be the amount of light.  I had my 100-300 out the other day (on my G3) in the backyard taking pictures of the many and varied birds.  I had it on a tripod, and used a shutter release, so there was no movement.  It was a grey day, and the zoom was probably between 200-300. There was numerous spots that the birds would stop and perch, so I waited for them.  Even though I shot Raw, and massaged the images as best I could (+ NIK), I was fairly disappointed with the results.