Thank you, very interesting! It seems that the bigger CPUs use a lower clock speed to reach the low TDP. Clever. I'll go for a 4 core i5-4590T, I like the true 4 cores instead of the hyperthreading, and turbo boosting to 3 GHz sounds reasonable... much more doesn't make sense anyway in real world applications because the memory is the bottleneck. But this CPU has quite some cache aswell.
Thanks again, I've ordered the CPU and parts to assemble the new machine... it will be a christmas present.