wireless speed depends on multiple factors. if the Speeds are fluctuating with ALE/Stellar AP it will be the same for any IEEE standard/WI-FI alliance certified AP in the same environment with same client.
Let me give some idea and see it helps as many details are missing like how many AP's, client used for testing etc..
Ensure the Wired client speed are consistent before testing the Wireless Clients.
Try to ensure you test with client which has minimum two spatial streams in 5GHz as 2.4GHz is more prone interferences.
Try to change Management Rates and Data Rates to min 24 if the test is conducted within 5 Meters from the way.
Disable the 80MHz if the AP’s in the setup are more than 5 AP’s which can see each other
Do not test the Wireless Speed standing Underneath the AP.
If you have still issues Please contact Local team to assist you or Open ticket with Support.
As recommended by thanjavuru, check first with a wired client. Many times is the WAN/MAN link which is causing the problem. Then with the same client (CPU, RAM, etc.) do the wireless tests.