XTOL Diluted 1:1 and Straight

If your testing results in too short development times with straight XTOL, then use the 1+1 or 1+2 dilutions. Dilutions are useful in dealing with plus and minus zone system processing. Personally, I use 1+1 and 1+2 dilutions, rather than straight XTOL.

I use 1:1 for two main reasons - longer, more manageable development times, and I get twice as much film developed out of a single batch.

The other reasons, more film speed, less solvent affect, sharper grain, etc., are really great and desirable to me, but I can't say that I've ever run a side by side test with full strength XTOL to see how visible they actually are. The two reasons I mentioned first probably have a bigger impact on my photography :) But I like to think 1:1 benefits my film in visible ways.

If you,perchance,have kept that used batch of Xtol stock you are pretty close to discovering the joys of 'seasoned Xtol'.
If you continue to use it,adding 80ml of fresh stock for each film,it becomes 'Replenished Xtol'
You can expect finer grain,higher sharpness,and higher economy than 1:1. The film I used to compare the two methods was Fuji Neopan 400. Two 5x7in prints from 12x16in scale enlargements proved the point to me.
You can read the threads on Apug.org for the finer points of replenishment.
Xtol should be just fine with any b&w film on the market.

Though Kodak no longer recommends it they used to tell us Xtol 1:3 was excellent. Having processed much 4x5, 5x7 and 8x10 film using it at 1:3 I prefer the dilution. Works well.