Prebaking bread, which internal temperature would you go for?
That should work, as 70C/158F is the gluten coagulation point. I'd probably go to 80C/176F because stollen's an enriched dough with many added ingredients (dried fruit, almond paste) and, as Athanasius says below, 75C/167F is where gluten is "completely set".

[I bake stollen to completion and then freeze them, but you probably have a reason why you want to parbake them. They dry out a lot in the freezer, so I'd love to know if parbaking them helps keep them moist. Can you let us know?

(Addendum. Mine dry out. That's probably because I use too much dried fruit (which absorbs water). (Addendum 2. Try dried Calimyrna figs in the stollen. They're not traditional, but they're wonderful in stollen and compliment the traditional orange zest/flavour and rum/brandy).

Source. http://www.thefreshloaf.com/node/14281/need-help-par-baking#comment-88647

He's quoting from Jeffery Hamelman, one of the most respected voices in bread.


  There is a number of things (happenings) while bread bakes that you
  need to consider. Since, you will only be keeping these a short time,
  and your freezing them, some may be more important than others.
  
  Overall, you want a stable product that won't change biologically,
  structually, or chemically while its being frozen, during thawing, and
  final baking, except for browning nicely.
  
  That means you want to complete oven-rise, kill the yeast,  coagulate
  the gluten, gelatinize all the available starches and stop all
  enzymatic activity.
  
  I'm using Hamelman's Bread, page 24, as a reference for the necessary
  internal temperature needed to achieve all the above. Yeast dies about
  140°F (60ºC), gluten coagulates between 158°F (70ºC) and 176°F (80ºC), i.e., oven-spring
  will cease, the dough will not collapse. Gelatinization and enzyme
  active is finished at 194°F (90ºC).
  
  To insure a stable par-baked loaf, I'd bake it covered for 15 minutes,
  as you reasoned, but I'd rely on internal temperature to assure all
  biological, chemical and structual changes in the dough were
  complete.Finishing the par-bake covered or uncovered isn't critical. I
  think reaching 194°F (90ºC) will assure stable par-baked loaves, and
  relatively low or no crust coloration.
  
  However, you may be able to get away with 9 or 10° less. An online
  source, states the well-known and well-respected La Brea bakery
  par-bakes bread to 185°F (85ºC), with satisfactory results.