Very good questions because remember Ohm's Law is theory and can not take into account equipment limitations. There are several factors probably not being utilized in the 5.0/3.0 and 3.7/1.7 discussion that can make a huge difference and why experimentation can result with such different results. Yes, experimentation has lead me to the following conclusions also.
First of all, all comparisons must be done on the the same PV, same battery brand/make, etc. for the following reasons.
All PVs have a different number of "touch" contacts or "solder" contacts in them. Each time there is a touch contact there is resistance. I had one PV (which I shall not name) that had so many "touch" contacts in it that I was losing upwards to 1 ohm in resistance. In other words, my 2.0 ohm carto now acted like a 3.0 ohm carto. Also, have you seen the expression "hot spring" on the board? The materials some springs are made out of are not as conductive as others. Normally not a problem but remember we are dealing with very minute electronics here and can make a huge difference.
Not all batteries are created equal. Basic 3.7 volt batteries are designed to provide about 1 amp of draw. There are some minor differences and I've had some batteries draw as much as 1.5 amps very well. But normally whenever you go over about 1.5 amps you really should be using high drain batteries in order to duplicate the same effect. Sure I've seen some people swear by this brand of battery but for the two setups we're talking about your really should be using high drains. I use 3.7/1.7 and 3.7/2.0 setups myself and I can see huge difference depending on which batteries I am using. The high drains will give you far more TH, vapor, flavor, etc.
Sorry, I couldn't think of an easy way to explain the theory behind DCCs. Just remember what they say about what the battery "sees" and that is how they will react. For me, I can't get a DCC to last more than 3-4 days and they do drain my normal batteries faster. I think because they actually don't run hot enough on each coil so they can self clean like a single coil will do.