Hey welcome to the forum, we love new people!
Cardstocks are really variable, there’s no simple answer here. You’ll need to test. Luckily, there’s a really good test method, check out #6:
You can get the exact answer for your cardstock in just a few minutes. 
I tend to cut cardstock at 80 power and the speed tends to be in the mid 300s, I find that limiting the power like this limits flashback. You can use this test method to dial it in exactly for your specific paper—set your power to 85 and float the speed.
As for gsm to pounds there are online converters. 220 gsm is about 150lbs: