I don't recommend trying smoke. I don't think many people have tried it, because it's pretty useless. Your computer case is small enough for you not to have to worry about that, and if it is a good brand, then it will have been tested for good air flow. I'm assuming that it is a new case you have. If you have less fans on your new case then less air will be entering the case. If your fans are smaller, then they have to spin faster to move the same amount of air. If you installed new components, then remember that they will produce more heat, and therefore will heat up the case a bit, because the case has to dispel more heat than normal.
If you've got the money, and are worried about the temperatures, then get water cooling, you can get some really good GPU and CPU coolers that are prebuilt, and only require you to fit them in the case.