On a dual CPU server, is it normal for one CPU to run hotter than the other

Recommendations on server room temperature vary greatly.

This guide says that:

General recommendations suggest that you should not go below 10°C (50°F) or above 28°C (82°F). Although this seems a wide range these are the extremes and it is far more common to keep the ambient temperature around 20-21°C (68-71°F). For a variety of reasons this can sometimes be a tall order.

This discussion on Slashdot has a variety of answers but most of them within the range quoted above.

Update: As others have commented below Google recommends 26.7°C (80°F) for data centres.

Also the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has recently updated their recommended tempature range to be from 18°C-27°C (64.4°F-80.6°F).

However this article agains highlights that there is still no consensus on the subject. As mentioned in the article I would highlight that:

...nudging the thermostat higher may also leave less time to recover from a cooling failure, and is only appropriate for companies with a strong understanding of the cooling conditions in their facility.

IMO most companies would not have such a strong understanding of cooling conditions and thus it would be safer in a small business environment to be running the rooms a little cooler.

NB: It is important to note there are a lot more factors to consider in a server/data room than just the temperature, air flow & humidity for example are also important concerns.

For that particular model the best performance is reached by using identical DIMMs in EVERY slot - although this isn't necessarily the cheapest or most future-proof option.