I've kept in touch with quite a few breeders who have crossed other Angora breeds in with their Giants for different reasons. Some people had French who were constantly going overweight, and Giants who were constantly underweight. Seems like a good idea, except that there is a difference in wool types, and French are medium-boned, you want a bigger boned breed if you are trying to improve your Giants. However, careful selection and culling certainly can result in a better Giant from this cross. Some people had English and wanted faster coat growth. Unfortunately, this cross usually results in loss of the lovely, soft texture of the English. It also softens the texture of the Giant. But again, careful selection and culling can bring the best of the two together. I personally like my Giants a little softer than what has become the norm.
By far the most popular crosses between Angora breeds are French/Satin and German/Giant. I won't go into the former, since it doesn't involve Giants, but I've done a whole lot of the latter, with mixed results. The following is MY OPINION, based on MY EXPERIENCE. Your mileage may vary.
The older German lines in this country, pre-2002 imports, benefited my Giants enormously. So did the first crosses with the 2002 imports. Then things started going wrong - at least with fertility and sickness - when I got really serious and chucked most of my older bloodlines for the 2006 imports. My opinion is the increased density (and documented coarseness) of the wool in the import bloodlines resulted in increased body temperature, similar to that of a fat (obese) rabbit. Fat rabbits don't breed well and aren't healthy, and neither did/were my rabbits, the more import blood they had. I looked at feed, I looked at housing, I looked at air quality, I looked at everything, until eventually I realised that none of those factors had changed, but the rabbits had. I've since gotten back to my older bloodlines, thanks to several satisfied customers, and my rabbits are breeding again. :) I have not totally abandoned the import bloodlines, the bucks usually perform well, and I still have one doe and one buck from them, but I've yet to get babies from either. Maybe because I'm breeding them together? I dunno.
So lately I've been using fuzzy French Lops for color and size, my old bloodlines for density and texture, and my Otter line to improve color. My Otter line tends to be small, soft textured, but incredible bodies and color. The plan is to blend the three bloodlines and wind up with the perfect colored Giant. My Blacks are there, the Otters are close behind. I've also brought some very successful REW Giant lines in.
Edit - I forgot to put my conclusion in regarding crossing Giants and Germans. :)
My conclusion is, a little bit of German blood is very beneficial. More than that, and you start having issues. My advice is to get a really good buck, use him a couple of times, then keep him around as a wooler.
Next installment - Colored Giants, genetics and history.