100% (if the manufacturer decides to go with 100% as the limit) will (typically) be the design/certified limit for a particular engine. Things like derating, the "real" red line (may be more than 100%), etc. etc. come into place.
As far as determining thrust, use the chart. All the indications you mentioned are interrelated to each other in an indirect manner (ie nonlinear) and vary with temperature and altitude.