E30 Zone

I've been having issues with my M44 converted E30 running too cool, so this weekend was going to pull the thermostat and swap it for a spare (unknown age) genuine BMW stat from my spare M44.
This morning a mate has given me a new Circoli thermostat and as I was testing the spare stat I had, just for the hell of it thought I'd bung the new Circoli stat in the pan of boiling water as well. I wasn't overly happy with how far it opened up after being in boiling water for 20+ mins compared to the genuine BMW one.
The genuine stat had opened up to pretty much twice what the Circoli stat had in a much quicker time. Both are 95 degree stats.

So which would you use, new Circoli or unknown aged genuine stat?

I'd go with genuine. I had major hassle with a cheap one which came on the car i'd just bought. It was very new but I was forced to drop the money on a BEHR one after some overheating...

Flawless now, even in this heat romping on it just to make sure.

Well it turns out my M44 already had an almost new genuine thermostat fitted so I doubt it's at fault. But I've fitted the unknown BMW stat just to see if there's any change.

I've never looked closely at a thermostat before but assume it should be fully closed when cold so no water gets through, other than the small hole??