How good a COM is, unlike weapons, depends far more on it's number than it's level. The number (660) means that it's got the highest and most numerous bonuses to skills. From what I've seen, the hundred's digit and tens digit both can be anywhere between 1 and 6. A 110 COM would likely have a single skill bonus at +1 or +2 while a 660 COM would likely have all three skill bonuses at +3 and one of the bonuses at +4. The +3/+3/+4 appears to be the maximum bonuses on a COM as I've been seeing level 55 COMs that don't break past that limit.
The level of the COM still has an effect. I was able to get a level 22 660 COM that three skill bonuses all at +2. I was also able to get a level 34 660 COM with the full +3/+3/+4 and the secondary bonus, of which I am still using with the character at level 61.
The secondary bonus on the COM seems to have a low chance of showing up on a COM, and seems less with a 100's or 200's COM. Even with a 600's COM it doesn't seem to show up too often.
Put together all the random chances and you'll have a hard time finding a 660 COM with the secondary bonus of any level. I would hazard a guess that level 50+ COMs can have a higher primary and secondary bonus than a level 48 COM.