Upload & Sell: On
Here's a few handheld shots I took today, wide open (f/4) and ISO 800. The first one with the flags is at 235mm x 1.4 = 330mm, and the others are at 300mm x 1.4 = 420mm. OS was on for the first three images, and off for the sh*t hawk.
The IQ is not quite as good as an EF 300/2.8L IS + 1.4x III, but it's generally quite acceptable. The zoom capability is nice. The first few flag shots I took were at 300mm, then I backed off a bit to get a better composition. YMMV.