I was wondering in particular about Wis. Do you gain an extra practice every even number of wis. For example going from 17 Wis getting 3 pracs a lvl to 18 wis 4 pracs a lvl.

It's more like this:

Practices Gained Per Level:
16 = 1 practices per level
17 = 2 practices per level
18 = 3 practices per level
19 = 3 practices per level
20 = 3 practices per level
21 = 3 practices per level
22 = 4 practices per level
23 = 4 practices per level
24 = 5 practices per level
25 = 6 practices per level
Note: Wisdom points achieved by items count as 1 wisdom point contributing to practices per level.

I recall getting two pracs/level as orc, and orcs have max 16 wis. This table, while pasted from Dios, isn't entirely correct IMHO.

You are probably right, but it's close enough for government work.

More wis in general equates to more pracs, but it isn't at evenly divisible number of wis.