I'd like to clarify something: a lot of the information on the wiki may be very old. Orcs were completely reworked at one point, they used to have 1+1 base attack bonus for 120 CP (that is, the first conversion threshold gave you 1 base attack, the second 2, the third 3, and so on). This meant that humans could actually surpass orcs for damage even at very low levels if you weren't converting much.
Orcs really needed to get above 600 CP to even be worth consideration. Back in the day, gold was way scarcer in purist runs; most dungeons had only one boss so there was no second trophy to redeem and you started with 0 gold if you went purist. As a result, purists basically had to go in with the presumption that they would never see more than 400 CP from converting four out of five of the glyphs. This made Orcs useless for purist runs, as humans completely outclassed them at these low CP levels.
With that history lesson out of the way, Orcs are now generally better than humans for Berserkers. Dungeons where hitting level 10 is unavoidable (VGT and Naga City in particular) that cause you to lose the higher-level-enemy attack bonus are the only places where human makes sense over Orc for Berserkers now.
Not sure what Gnome Berserker does that Halfling Berserker doesn't. Seems like one of those PQI-exclusive combos. Elf Berserker is dependent on Mystera to be useful, and not so much outside of that.