A temperature recording device - whether it's strips, a temperature gun or a donut probe, will definitely assist you in determining temp settings and belt speed.. You will need to try different settings and record your findings. As you mention plastisol - most ink manufacturers will want you to get the temp up to 320 degrees to cure. Many elements effect your dryer temp and curing : heat/humidity, color of shirt, and fabric type of apparel. to name a few. When it comes to the 300 per hour, it is fair to ask a manufacturer how they got to that number. Have a great day...