Assume you like the look of your beautiful posted gallery photo, and want to obtain that look naturally, you are right to plan to "underexpose" and "overdevelop".
But Dektol straight is going to be difficult to control.
The day I did my tests for Dektol 1:9, I also did snip tests at 1:5 and made a note to myself that 1:5 is too difficult to control. I got densities over 2.0 in 5 minutes and really I don't want "black" negatives for Silver Gelatin printing on Grade 2 or 3 paper.
At 9 minutes, I achieved a "normal" contrast for Tri-X 35mm with Dektol 1:9. This verifies the rule-of-thumb that PE told me about (1 minute per part of water). So keep that in mind.
For higher contrast, develop longer or at higher concentration than I did. I'd guess a couple fewer parts of water or a couple more minutes.
In general, developing film to high contrast requires MORE control if you want assured results. Mr. Ford, my high school print shop teacher (imagine John Wayne with librarian's half-glasses), used to look down on us and call us pinheads if we came to him for advice when we forgot to include a test strip in the camera shot. Because a bad shot with a test strip, is easy to count out the half f/stops to the correct exposure. But without a test strip, you (and the teacher) have no idea how far off you are.
When shooting high-school newspaper pages, a test strip can be in every sheet of film. You just cover it up when making plates. But when taking photographs, you want all the film for your picture. That's why it's more practical to do tests on separate sheets of film.
Test or not, it's up to you... I'd test... or put a grayscale in every picture.