The SF25 comes with an afterburner. Both are mighty fine machines. I've roasted on both, though not an IR with an afterburner. It would be a tough decision, but if I were making it, my 2 cents would be to lean toward greater volume capacity, since you're facing outgrowth. The SF25 has more usable capacity, while the IR tends to cap out good tumbling and airflow at no more than 80% of the rated capacity, depending on the coffee.