How does accepting a full time lectureship position at a top 15 University affect one's chances of future employment?
Lecturer positions tend to overwork you in courses such that research time is little to none.  If you really want a tenure track position at a university with a research focus or semi-focus, you need to continue publishing in quality journals.  If such is the case (in your scenarios 1-2), you may consider a postdoc research position instead.

If scenario 3 or 4 is your ultimate goal, get good teaching marks and recommendations is paramount and a lecturer position is ideal.