If you have a perf app that can output solid data (or good manuals) pick a weight and temp, nil wind.
Get a spreadsheet, for each 2000' from FL280 to 400 determine the total FF and the CAS. Use an online calc to get the TAS which then equals GS. Do this for various cost indices.
Then plot the SGR across the X axis and alt on the Y. Gives a good feel for why optimum is optimum, what the effect of wind does (add / take a few kts from the CAS and see the effect). Quite powerful. You can see the delta kts to make a climb worthwhile.