I went under and was about 16% bf when I went in. Had been training for many years. Mine were unders, and then I started training for my first bb comp 3 months later. It took me about a month to have full range of arm motion and I was still being careful about driving -- just hard to do the check behind before making lane changes, etc. When I first started training for my bb comp (followed 16 weeks later), my chest was very tight. I explained what I wanted to do to my doctor, citing that I had been able to get that pec split in the past. He assured me that despite the cut in the pec muscle, it would not affect my ability to build those muscles.
It took awhile to comfortable be able to press anything significant. Basically it has to do with getting any scar tissue broken up / getting the implants "comfortable" in their spots. It was like trying to work out really tight, sore muscles. Occassionally I would get some funky muscle twitches while doing pull-ups and some back exercises towards the ends of sets. After about a month of "working out" the tightness in my pec muscles, it was no problem.
I can see the doc's point about "overs" show the ripples, etc. at really low bodyfat. When I hit 10% and lowerI could start to "feel" the edges of the implants on the outside edges. You just really become aware of how thin your skin is as you start water depleting too. They would sort of hurt sometimes - not due to anything wrong - maybe just the weight of them with the thin skin.
Somewhere along the line I heard that DD's weight 4 lbs total -- mine are D's - so I guessed that I added another 3 lbs to my chest. Your center of gravity shifts a little, so you might become aware of sore lower back sometimes, and the weight of them sometimes really seems apparent as you dry out the subcutaneous water pre-contest, but its not bad. You also seem to be able to feel the edges of the implants at very low bodyfat. I never noticed any ripples. The only really weird thing about unders is you will notice a sort of funny pull on the skin when you flex your pecs. You'll know what I mean. Its not bad, just kinda weird.
You might ask your doc if she has another patient who is a bb/fitness person who might be able to call you and give you some insight. I would also check out the chat room at
www.implantinfo.com or the discussion forum and see if anyone else there has some experience there.