Hello Marko,
You've certainly gotten some great advice from Christopher and Donald. Another option you may want to consider is the method taught by the late Fred Picker for use of Zone System and 35mm/roll film; that is, after determining proper film speed, pick a high value zone--most use Zone VIII, but quite a few great photographers like Alan Ross are recommending calibrating development to Zone IX these days--and get your development time/temp set. In the field don't worry about +/- development, etc, simply place your high values where needed, check your important shadow (adjust to taste), then expose and develop per your test above.
Fred always preached to get the exposure as far up the curve as possible without blocking up your high values. Mid-tones and shadows will fall where they may. As I said, nothing is set in concrete...many times I'll give a little more exposure if my shadows are teetering on the edge. Sure, this pushes the high values a little closer to the shoulder, but not to worry (especially with Tri-X) exposure affects the shadow values much more than the other end of the curve. I've used this variant on the Zone System for years with MF and never had a problem. If the SBR (subject brightness range) is too great, then you must decide if you want to favor the shadow end or high end of the curve; or, use other methods such as filters to adjust the overall brightness range.
Hope this helps. Happy shooting!