Running the multi-threaded intense ray-tracer pushed the Core i3 2120 operating temperature up to 55°C, which is in line with the other CPUs, but the quad-core Core i5 2500K was elevated to 60°C.
The system power consumption with the Core i3 2120 CPU was 69 Watts (same as the i3-2100) while the Core i5 2400S averaged to 82 Watts and the Core i5 2500K was up to 100 Watts with this Intel Z68 system.
The Intel Core i3 2120 is an interesting processor. It really doesn't bring too much to the table besides pushing the frequency to 3.3GHz, which is great as long as your targeted workload is more limited by raw clock speed rather than core count. In common Linux workloads, the Core i3 2120 was about 6~8% faster than the Core i3 2100, which is clocked at 3.10GHz and thus right in line with the elevated 6% frequency boost.
The non-K Sandy Bridge CPUs have their multiplier locked and don't overclock too well, so if a higher frequency is of use to your needs, the extra $10~15 USD for the i3-2120 model is worth the cost. However, if you are considering the Core i3 2120 for gaming or any computationally intense tasks, you are better off with a K-variant Sandy Bridge. Besides the unlocked multiplier, the Intel HD 3000 graphics are a measurable improvement over the Intel HD 2000 graphics, as today's results show.
The Intel Core i5 2500K carries a retail price of around $220 USD, which is about $90 USD more than the Core i3 2120, but delivers an excellent bang for the buck as these Linux benchmarks indicate.