I've had a go at TasZero's suggestion of using VirtualDub for making animated GIFs.

It works pretty well; the proceeding of the image sequence is fairly convenient. The downside however is that VD seems to have no option to edit the delay-time of each single frame, which any decent GIF-software should allow. Furthermore, VD doesn't support WMA-files, which is a bit of a bummer, but not an essential one.
The good things are the image sequence export and the option for changing the frame-rate, making the GIF creating process much less time consuming.
So the GIF below is the result from using both VirtualDub and Animake (VirtualDub for saving the image sequence; Animake for editing each frame's delay time and for converting the whole thing into a GIF:
No loop here, but the GIF's speed is conform to the source videofile (which is 'Ravex In Tezuka World' btw).