How much difference is there between these two at idle?
Its for a storage server so 90% of the time, it won't do any work.
My idea is that the power compsumtion is the same, until the 4130 exceeds the clock of the 4130t?
Yeah pretty much, don't buy the T unless you are thermally constrained: fanless, confined space, etc. I think a lot of people psych themselves into paying the same for a slower T model when they don't need to. When it is time for it to actually do work, you'd rather it be able to ramp up high and get the job done faster.
(sometimes this design approach can actually save
power because it can race back to idle even sooner, but anyways...)
Going by what I've seen and other people have shared on various forums, the idle difference between T and non-T is like the variance between cpus of the same model, aka practically margin of error.
Overall Ivy and Haswell idle very well, even my S2011 gamebox w/ 130W TDP Ivy-E is chilly just reading email or whatever.
I did buy an i3 3220T for a fanless router and looking back I don't even think it was needed there, if I built another one today it would get a standard i3.