Well, without anyone else commenting this is becoming a personal memoir "stix's hilarious adventures into the world of C# with Arduino".
I'm on vacation, with only intermittent access to the internet, so its been hard for me to post. The changes you made to receive serial data are reasonable. When I wrote the code, I was not interested in sending huge amounts of data. For sending temperature and humidity data, for instance, sending data once a second is far more often than needed. Since you have different needs, changing the code is reasonable.
Actually displaying the data in a text box is NOT the best way to receive lots of data as fast as possible. Write that data directly to a file.