I haven't used the old 105 much, but not too long ago got my wife's old 105/2.8D back from the fungus doctor, and find it not bad for bug chasing. The focus is a little slow, but it works. Still pretty early here for interesting flowers and insects. At least there are dandelions.
On the way back I ran into a robin, fiercely guarding her nest. Every time I come by she swears at me in angry fluent tweets.