Poolmining is never completely reliable, especially if there's vardiff which will always fluctuate. But even with fixed diff you'll have to run it for a long time to be sure.
--benchmark had plenty of issues in the past so I've stopped using it so I'm not sure how it is recently.

For checking speed only, I personally like to just solomine to any local wallet, doesn't even matter if the algo is different and just check the reported hashrate.
Stable clocks and fix fanspeed recommended.

Regarding aluminum cases, I'm also curious how much people who own them paid for them.