Here a few things I will assume:
Your Anorith/Armaldo is often a few levels behind your opponents, because of its erratic leveling rate. It's level 41 when battling Cheren, level 48 when battling the Elite 4, level 51 when battling N, and level 54 when battling Ghetsis.
It has 16 IVs and a neutral nature.
You fed it a bunch of carbos because you care about its speed, so it now has 164 speed EVs and 64 EVs in all its other stats.
If all of these assumptions are true and you keep it as an Anorith, its speed stat will be 89, 104, 110, and 116 when you battle Cheren, the Elite 4, N, and Ghetsis, respectively. If you evolve it into Armaldo, its speed will be 65, 75, 79, and 84. Thus, these are the opponents that you can outspeed only if you keep your Anorith unevolved:
Cheren's Emboar and Samurott
Grimsley's Bisharp
Caitlin's Gothitelle
Shauntal's Chandelure
N's Vanilluxe
Ghetsis's Seismitoad
If you use X-scissor, rock slide, dig, a hard stone for Shauntal, a silver powder for Ghetsis, and an expert belt for everyone else, these are the opponents that will take less hits to knock out if you evolve your Anorith:
Cheren's Simisear (2 -> 1), Simipour (3 -> 2), Emboar (3 -> 2), and Samurott (4 -> 3)
Grimsley's Scrafty (4 -> 3) and Krookodile (2 -> 1)
Caitlin's Sigilyph (2 -> 1)
Shauntal's Cofagrigus (4 -> 3), Golurk (5 -> 4), Jellicent (3 -> 2), and Chandelure (2 -> 1)
Marshall's Sawk (4 -> 3) and Mienshao (4 -> 3)
N's Carracosta (4 -> 3) and Vanilluxe (2 -> 1)
Ghetsis's Seismitoad (3 -> 2) Eelektross (3 -> 2), and Bisharp (3 -> 2)
I haven't even calculated the number of opponents that would take more turns to knock out an Armaldo than an Anorith.
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Tldr evolving a Pokemon is usually a good idea.
