I'm not sure, but let's call the green ones the bc2500 and the blue ones bc 2250:
Both comfy, well contoured boots inside. For all the support the respective cuffs deliver, the weak point is the lack of torsional rigidity down through to the end of the boots and ultimately the ski. This is where a boot like the plastic 75mm Garmont/Scott Excursions or Scarpa t4s are so strong - great flex at the bellows, and fantastic torsional rigidity.
Also, fit is pretty important. The higher 2500s that I have are slightly large on my foot, so the break point, above the ball of my foot, is nice and far back. I can almost leverage the extra length like a 75mm duckbilled boot and I can really keep the ball of my foot flat on the rear ski. The blue 2250s are a size and a half down, and they break too close to the end of my foot and consequently I'm up on my toes more, making for a squirrely back foot experience, as discussed in the NNN BC Technique thread.
.