Looks like it runs a couple of degrees cooler with the case open. I would take some cardboard and tape and cover up the hole where the side panel fan was so that the rear fan draws air from the front of the case. Having a hole in he side panel after removing the fan disrupts the strength of the air flow from front to back. You might also consider putting a stronger fan in the rear panel.
The other thing I would definitely do is remove your CPU cooler and redo the thermal paste. Of course, this assumes you have some extra thermal paste around. If not, go get a small tube of Arctic Silver 5 or Coolermaster MX2 or MX4. Don't apply the paste like the cooler manufacturer says to do it. There is a better way with those exposed heat pipe coolers. First, get two or three paper coffee filters and some isopropyl alcohol. Wipe off the old paste from the CPU face and the bottom of the heatsink. Get the bulk of it off with dry coffee filters and then finish the job with one moistened with a little alcohol. Coffee filters are great for this because they have a hard sheen and don't leave insulating fibers behind.
Then apply the paste. Don't use the "pea-sized blob in he middle" method. That sometimes doesn't work well with the exposed heat pipe coolers. The ridges between the pipes sometimes keep the paste from spreading. Do this instead:
First, squeeze a tiny line of thermal paste along the sides of the copper heat pipes at the cooler base. Take a putty knife, razor blade or plastic credit card and swipe across the cooler base back and forth with downward pressure to force some thermal paste into the groves along side the pipes at the cooler base. This is called "tinning". Then apply two thin lines of paste across the base so as to divide the area into approximately equal parts (see attached pic). Don't try to spread the paste with anything. Next, just lower the cooler onto the CPU and clamp it down, using a back and forth "X" pattern as you tighten the screws a little bit at a time. Allow the clamping pressure to spread the paste. Make sure the clamping screws are fully tightened. Good pressure between the heat sink base and the CPU face is essential.