According to Jay Mitchell, an expert in the field, you only need about 20ms to capture the actual cab. Everything after 20ms is room reflections, and you need far more than 170ms to capture the actual room, so really it’s just added noise. I personally feel I get better results using the “Normal” 20ms IR + one of the great reverbs. There was a thread or two on here, I believe started by Cliff, talking about some of the benefits of shorter IR. After a fair amount of personal experimentation I think it’s a non issue. YMMV