Smarter people than I have recommended ~90% VO2max target. See previous post for references
To repeat what I wrote then, the difference on long-term performance outcomes of training at 90% vs 100% has not been conclusively shown. The literature recommendation is based on acute response studies.
Since then I was referred to this study showing no difference in TT improvements after training at 95% vs 100% of vVO2max, matched at 60% Tlim/TTE @ target intensity. Although as always there were some methodological limitations. At least suggests no difference from spending less time at higher intensity, vs longer time at lower intensity. all wrong. Kept for posterity, Does not show this result and suggests training at 100% may be more effective than training at 95%.