I am currently planning a mission for regarding the extraction of physical files from a librarium installation in a Hive City on Casobel that is currently in the thralls of the Tyranid invasion. I am looking at utilizing the retrieval of the data as primary objective with secondary and tertiary objectives going to supplementing the beleaguered forces of the city in fending off the nid swarms. Each tertiary objective completed would yield a range of "victory points" that go toward reaching a benchmark value that could dictate whether the hive is overrun or if the kill teams interventions may have staved off the inevitable for just a bit longer. An example of such an objective I have been thinking of including is the repulsion of 2-3 Carnifexes trying to breach a primary gatehouse with success yielding 2-3 points. Failure would require the KT to pursuit one or both carnifex to prevent contamination of a major water purification plant with success then only yielding 1 point.

I was wondering if anyone has utilized such a method as this or know of a supplement that can provide a good insight into how well this method would work to illustrate the KT's impact on the battle?

Oblivion's Edge, I think, there is a turning point system for gaining extra guard reinforcements, seems like you may be able to adapt it.

Have you looked at the kill marker system in the core rulebook? Not as detailed as what you're looking for but it is a rule many overlook.

Turning points are a great idea. The ones I've seen are from Mark of Xenos - and I like them a lot

I had great fun with the turning points in the sample adventure "Final Sanction". Gets the players focused on how to win battles, not just individual fights.