I have them both and a 20D.
My reasoning for getting those lenses were:
1) First and foremost: excellent image quality (I'm happy to confirm this).
2) Relatively (indeed, this is so relative...) light weight and moderate size if compared to the f2.8 equivalents
3) With modern cameras you can dial up the ISO quite comfortably in case you run into a situation where the f4 maximum aperture doesn't seem to cut it. The 20D really excels in this regard. This was true already with the 10D but even more so with the 20D. IMHO, of course.
However, in case you're really serious about shooting indoor sports or such events, there's no substitute for wide aperture lenses. I shoot mostly nature and landscapes (I use a tripod and have the luxury of stopping down the aperture as needed) and so far the f4 versions have suited my purposes very well.
Of course, there are some other exceptions to this, such as astrophotography (and even there the full aperture is not always required) etc, but for general shooting I'd say those two are very fine lenses.
Wider apertures offer shallower depth of field in case that is required (shallow DOF is often required for intance in portraits, where you'd typically use a short tele), but the 70-400 f4L is not too shabby in this regard either.
Maybe you could try out various options in a store and make up you mind after that?
Just my random thoughts, I hope you end up with lenses that suit your requirements the most.
Earthlight
Hi
Are they a good choice along with 20d? Could someone post sample
photos using these lenses?
Thanks!
regards