Once you have chosen your target TSS (example : 280 TSS), then you still need to find the more realistic association IF / Time
Is it 66% IF over 6h30 ?
Or 69% IF over 6h ?
Or 59% IF over 8h ?
Simulation is nice, but testing in similar conditions is better, if you can.
You can test you on just 1 or 2 hours, on a relatively similar course (% uphill and downhill, altitude, wind, …) to see what speed (so what realistic time) you can expect at some given % of IF. This will help you choose the right targets % IF and time.