I only mentioned it because you mentioned IAS and IAS speed loss. I can say it also depends on your altitude you are climbing to. I've flown light to heavy jets and this is the typical behavior i've seen in regard to climb performance. In regards to optimum, I have always been in operations where you climb to 2000ft above optimum. If step climbing, I hang out till 2000ft below and repeat the process. If doing a constant cruise operation, again, I plan 2000ft above optimum. In these cases, I fly the recommended climb speeds and don't stray too far from it even if in a hurry. I've watched guys climb at too fast of a climb speed and couldn't make it until they reduced speed. On average when near optimum and above it, I see climb rates of 500 to 800 feet per minute. When climbing up to the aircraft's service ceiling, its about 300 feet per minute. When I see these type climb rates, I know i'm in the optimum altitude range and approaching the aircraft's performance limits. As you know, you don't want to be below the 500 feet per minute mark for ATC reasons. Here's a good real world operating tip. When climbing in mach in close to optimum, the plane tends to get pitchy when in VNAV or FLCH. When the plane starts to get loose in pitch, we select vert speed to settle it down. When in vert speed, you work the vert speed to maintain your climb speed. You can get in trouble really quick if you let the plane pitch too much. If you get behind the thrust curve, it can take a long time to get back on speed and climbing again. Plus the pitching gets aggressive and leads to overspeed or stalling. If the 737 is climbing correctly, these are good rules of thumbs to fly by.