Hey Buddy,
Sounds like a great distance:vertical ratio there, which event is it your are doing?
If you have done something similar before I would have a look at your heart rate data for this on how long you were sustaining outputs. 170bpm is likely high zone3 for you and to sustain this for several hours would take a serious amount of carbs and muscular endurance!
I would suggest that is you are ticking all your boxes for training and working hard, that racing by feel/effort would be good for you as on race day the heart rate can be allover the place with adrenaline, excitement and nerves. If you are highly efficient you will likely recover a bit on the downs, your HR will spike up a bit on the climbs and then for everything else I would aim to race for that distance at upper end of zone2 or as close as you can too this probably also a bit into zone3. This would be purely from a fuelling / sustainable energy output as you want to be burning mla better mix of fat and carbs, and avoid too much lactate build up which I am only guessing will come fast if you try to average 170npm on a mountainous race of that distance.
The crazy thing is everyone’s cardio systems are so varied. One of my friends does his 6 X 10min efforts in a heart rate range of hifh zone 4/into 5 which technically is burning on borrowed time according to uphill athlete protocol of sessions for effective time in that zone but he is still seeing solid results. Just listen to your body dude and focus on slating the competition around you!
Hope some of that helps 🙂