Don't understand it. The system is just out. And for now, the 7800 Go will be sufficiant for most, or maybe all games.
Why already upgrade. Be patient, and within one or two years, there is a nice mod available, tested and prooved. Then you upgrade.
I believe it would. Even my I8600 has CPU+GPU+RAM+HDD temperature sensors. [Please make *sure* you spell sensor correctly - "censor" has a completely different meaning as opposed to "sensor".]
If you really want to confirm the presence of CPU+GPU+RAM+HDD temperature sensors within the I9400, get someone who has recently bought an I9400 [and delivered] to run I8kfanGUI or whatever the equivalent program is called.