Here's a summary of the different species in homo -- note the brain volumes. (I didn't mean to say all were intelligent, just that they were all near-human and went extinct, but the Neanderthals were likely more intelligent.)
And here:
Neanderthals, according to Jordan (2001), appear to have had psychological traits that worked well in their early history but finally placed them at a long-term disadvantage with regards to modern humans. Jordan is of the opinion that the Neanderthal mind was sufficiently different from that of Homo sapiens to have been "alien" in the sense of thinking differently from that of modern humans, despite the obvious fact that Neanderthals were highly intelligent, with a brain as large or larger than our own. This theory is supported by what Neanderthals possessed, and just as importantly, by what they lacked, in cultural attributes and manufactured artifacts.
The WP table you link to gives these cranial volume ranges: H. sapiens, 1000-1850. H. neanderthalensis, 1200-1900.
Given the size of the ranges and > 70% overlap, the difference between 1850 and 1900 at the upper end doesn't seem necessarily significant. Besides, brain size correlates strongly with body size, and Neanderthals were more massive, weren't they?
More importantly, if the contemporary variation for H. sapiens (i.e. us) is all or most of that huge range (1000-1850 cc), do we know how it correlates with various measures of intellectual and other capabilities? Especially if you throw away the upper and lower 10% of variation.
I really liked Robin's point that mainstream scientists are usually right, while contrarians are usually wrong. We don't need to get into details of the dispute - and usually we cannot really make an informed judgment without spending too much time anyway - just figuring out who's "mainstream" lets us know who's right with high probability. It's type of thinking related to reference class forecasting - find a reference class of similar situations with known outcomes, and we get a pretty decent probability distribution over possible outcomes.
Unfortunately deciding what's the proper reference class is not straightforward, and can be a point of contention. If you put climate change scientists in the reference class of "mainstream science", it gives great credence to their findings. People who doubt them can be freely disbelieved, and any arguments can be dismissed by low success rate of contrarianism against mainstream science.
But, if you put climate change scientists in reference class of "highly politicized science", then the chance of them being completely wrong becomes orders of magnitude higher. We have plenty of examples where such science was completely wrong and persisted in being wrong in spite of overwhelming evidence, as with race and IQ, nuclear winter, and pretty much everything in macroeconomics. Chances of mainstream being right, and contrarians being right are not too dissimilar in such cases.
Or, if the reference class is "science-y Doomsday predictors", then they're almost certainly completely wrong. See Paul Ehrlich (overpopulation), and Matt Simmons (peak oil) for some examples, both treated extremely seriously by mainstream media at time. So far in spite of countless cases of science predicting doom and gloom, not a single one of them turned out to be true, usually not just barely enough to be discounted by anthropic principle, but spectacularly so. Cornucopians were virtually always right.
It's also possible to use multiple reference classes - to view impact on climate according to "highly politicized science" reference class, and impact on human well-being according to "science-y Doomsday predictors" reference class, what's more or less how I think about it.
I'm sure if you thought hard enough, you could come up with other plausible reference classes, each leading to any conclusion you desire. I don't see how one of these reference class reasonings is obviously more valid than others, nor do I see any clear criteria for choosing the right reference class. It seems as subjective as Bayesian priors, except we know in advance we won't have evidence necessary for our views to converge.
The problem doesn't arise only if you agree to reference classes in advance, as you can reasonably do with the original application of forecasting costs of public projects. Does it kill reference class forecasting as a general technique, or is there a way to save it?