I have a 2005 Quickrod and have played a 2018 fully loaded Quiclrod. There is a huge difference in the tone and feel. IMHO, the new Splawns are less aggressive sounding. My amp, vs the 2018 that I got to play, has slightly less gain but sounds meaner. Scott smoothed out the top end to my ears. Now the 2018 clean channel was far and away better than mine. On my amp, the lead channel gain knob effects the clean channel headroom. I run Gear 3 OD1 as my main tone with the gain at 1:00. If you have heard any of my videos, they is where the gain is set unless otherwise noted. Anything above 11:00 and the clean channel clips to the point where it is useless to me. The tone knobs on the clean channel of my amp also effect the tone of the lead channel. Move them off of noon and the tone of the lead channel suffers.
I have not gotten to play a Nitro, so I cannot really say about those amps. Just my experiences with the Quickrod.