A. My kids are both taking French (to be honest living where we are there isn't a 100% english option but there are variations on how much french they get in a day between the 4 public boards).

B. I don't have any empirical evidence.

C. Some of these points don't apply since you're talking about a combination gifted/immersion program but I'll include them anyway. This is often debated and discussed on Canadian forums and the basic summary is -
- in parts of the country where immersion is a choice (as in there are a small number of immersion schools in a large city and people choose to attend) immersion is used by many as a substitute for often non-existent gifted programs. People generally don't stick (or keep) struggling kids in immersion. It tends to attract involved and/or smart parents who often tend to have smart kids. This is generally seen as a good thing and while the classes aren't exactly gifted, generally there isn't the same degree of variance that you would see in a typical classroom. That said, a truly gifted program would be even better in this regard. Potential downside to this can be decreased diversity.
- in cities like ours where immersion isn't really a choice then the above doesn't apply. It is often just something else that accentuates the differences in learning speed between a gifted kid and average.
- the one possible downside that I've heard is that some gifted kids get frustrated when they don't have the vocabulary to discuss a topic at the depth that their gifted brain wants to. Personally we haven't run into this yet but I can see this potentially happening next year when science switches to french for DS. However, to be totally honest he hasn't been able to discuss science at school to the depth that he would like for the last 3 years either because a) teachers don't have time and b) he knows more science than the teachers do anyways (ok I'm being a bit of a smart a** but this is a kid that eats and breaths science. He watches science shows whenever possible, he has been known to try to read university text books and he has two engineer parents that have answered his never ending questions since he started talking so the elementary science curriculum is not exactly cutting edge for him). The way we look at it, at least he will be increasing his french vocabulary next year while reviewing basic science....
- positive - they get another language. Depending on where you live, travel plans or future career choices it might come in handy.
- positive - this is the one area where teachers are the undisputed experts over my kids (and us for that matter) and my kids do LEARN something at school. DS is very math/science focused and we're happy to have something that he actually has to work at a bit to learn (he isn't really seem to be gifted at picking up languages).
- potential negative - I have a few friends that went all of the way through in French but then struggled a bit in first year university because they had done technical things like chemistry, physics, calculus in french but were taking them in english in university. They all did well in the end but it took a bit of extra work at first to map what they were learning to what they already knew.