I don't have the same dilemma (immersion vs. gifted) but am also in the process of choosing which school (middle) to accept for DS & DD. Given their age (10), I am giving them the final say but have provided all the pros and cons as well as encouraged them to compile their own pros and cons. Too bad there isn't a crystal ball so we can see where they will be happiest!
Anyhow, you appear to have thought through the issues really well. Based on what you have written, it does seem like your younger DD should go for the immersion. As for your older DD, I do agree that it may not be wise to pass up the immersion given your sense that your older DD may not meet the minimum entrance requirements for the gifted program, however wonderful of a program.
You do seem to know your DDs well so go with your gut. I don't mean to imply that your older DD is not at the 145 level(technically EG?) but I do agree that it may be very difficult to tell without the actual scores. Your examples concur with what I have always observed about some teachers/others' declarations regarding my own children's giftedness - it often seem to me that it depended on your interpretations.
Anyhow, I know your pain. The only comfort I have is to believe that there isn't one right school and that the final decision will somehow work out. Good luck!
