Remember that not all TSS is created equal.
An hour at around FTP, so a TSS of 100, would be brutal for me. Four or even more hours at 70% of FTP, i.e. still in Z2 for both power & HR, so TSS of 240 upwards would have negligible effect. I’m assuming decent refuelling and hydrating for both scenarios.
I find the TSS calculations to fall apart once you get to long rides, by long I mean twelve hours or more.
You don’t say what your “big days” involve: are they a weekend of multiple crit style races; a two day grand fondo; a point to point charity ride? If you only ride crits and you are aiming at long days then time in the saddle will be important for comfort, etc.