In particular the 4670T which is a Core i5 quad core at 2.3-3.3GHZ at only 45W. This is quite impressive considering my mobile Ivy Bridge quad core has the same TDP.
Im not surpriese of the similar TDPs, they have almost the same clocks, Intel Haswell Core i7-4700MQ, 2.6~3.4GHz, you even get higher clocks on the mobile + hyperthreading.
Personally i dont think any T is worth it unless you dont have the cooling to handle a standard 4670, its just a nerfed CPU from factory, there is no specially low voltages nor cherry pick cpus, its just like buying a lower end cpu for the close to the same money you spend on the normal, but your cpu is less capable. I made the mistake of buying a 2100T, but i got it on release, i though it was really a special CPU but to my missforutune is just a nerfed 2100 that comes with an intel low profile cooler, never will be again a T or an S, unless they have something different.
All haswell CPUs will downclock to the same 800mhz on idle, most will draw similar power and heat up similar, its on load where each will different, but in the case of the T probably wont heat as much but wont do stuff as fast, so at the end is your choice, your money, but personally i dont recommend T or S versions, unless the build doesnt allow a cooler to keep up with the CPU.
Hmm, my experience with low powered CPUs has been always the opposite. Processors are generally "binned" and the better ones can either run at a higher clock speed, or can run at a lower voltage and consume less power, with a sacrifice in clockspeed.
Just looking at the chart I posted contradicts your claims. The easiest to way to see this is by comparing the 4400 and 4430 with their T counterparts. I chose these two because the specs between the regular and T version are exactly the same: same Turbo Boost, same GPU clockspeeds, same cache, except for one thing, a difference of 300mhz in the base clock speed. Yet, the difference in TDP between the regular and T versions is a whopping 19W. Have you ever overclocked a system? A simple increase in 300mhz will not increase your power consumption by 19W, that's for sure. The T chip uses less energy because it's a better binned chip.
Anyway, I am somewhat on your side that the S or T chips might not be worth it. But I don't know if so, and that's why I want to see comparisons, hence this post.