FL280 was the best TAS altitude on the 767 (330/0.83 from memory). I think it would be similar for the 737. FL300 for the A330. Used if I’m running late and/or I can get my snout in front of the preceding aircraft and beat them in.
On the classic the difference in TAS between FL290+/- and FL350/FL370 was substantial, from memory some 20-25kts which when combined with the expected far lesser headwind really added up.
On the NG only a couple of knots bonus in TAS, overall have to be a substantial gradient to make the exercise worthwhile especially if you could be sipping fual at FL410.
Cheers