Let me start this off by saying that I am in no way the final answer on this, but I think it's and interesting question...and I think I understand how this relationship works; so here we go.
The answer is both...kind of.
The ir/cab block does not contain any information on these parameters. The ir is simply a static filter. Having said this, a particular speaker type will have also have specific comp and time constant parameters associated with it even though the ir doesn't capture this information. In real life, an alnico jenson speaker may have different parameters than a celestian greenback, and so on. For an authentic representation of a speaker, these parameters need to be modeled. The speaker comp and time parameters found in the amp block take into consideration certain things like hi and lo frequency resonance found on the speaker page of the amp block. There is also the "motor drive" and "motor time const" parameters found in the cab block. These simply model the effect of high power levels on the speaker. It is safe to say that the parameters found in the amp block provide the most realistic simulation.
It is my guess that these parameters would vary greatly even among similar speaker types, so ...even though these parameters will alter the sound a little, in my opinion it is far more of a feel thing than anything else where these adjustments are concerned. So set them where they feel and sound right understanding that the parameters adjust how the amp responds to a specific speaker, or speaker type.
Please correct me if I have given any bad info here....