Hi, i'm currently without a teacher, so i hope some one could advice me on the forum.
I have been using Bach inventions and Sinfonias as piano sightreading material. It is the most challenging material i have faced so far; every thing else looks rather easy after a couple of sessions of Bach.
When executing Bach, its nessacary to perform lots of silent finger exchanges, which i'm becoming versatlie at, but is it ok, if i find it unavoidable, to break the legato by actually coming of the keys to get a better finger position, or does that make for poor piano playing.

If it's sight reading I wouldn't worry about it too much as long as you are not constantly in a poor position.

I agree with sboa that, if it's purely for sight-reading purposes, then fingering is not the main issue and I wouldn't worry about it.

However, a useful exercise might be to try playing it in a very detached style and then the breaks in legato, if any, will be less obvious.