[LAD] jack transport change accuracy for looping

Just wondering if I understand this correctly. I making a loop based app for step sequencing. When I previously did this in Csound, I clocked it off a phasor, so the timing was sample accurate ( but that brought all it's own issues to be sure ). I'm wondering whether I should do the same thing in jack app, or use the jack transport clock, or some hybrid. My question, am I correct in understanding that if I use the jack transport position to rewind in time, I'll get: C) any other clients with running audio looping back to ( may or may not be desirable ) B) a jitter based on the amount of time left between when the loop should end and the end of the frame buffer in which the loop length runs out? Has anyone solved B? Could it be done by some complex tempo cheating trick? Does anyone have any methods they've used for tight timing of looping in a jack app? Pointers at code appreciated of course. =) thank! Iain