You can make 16x24 prints from less than 6MP images.
I don't think anyone really knows where the limit begins and ends, in regards to megapixels and enlargements. Some have claimed that they've seen fantastic 4 foot wide prints from 2 megapixel images, some have a very technical and rigid interpretation based on megapixels and ppi. Indeed, some specific images may resolve better than others on a technical basis, but it might be too much of a generalization to judge the quality of the output in regards to the megapixels and subject only. I agree with everyone who says that the bigger sensor would yield a more detailed print... but really, this is no more insightful than saying that the grass is green.
I'm not saying that anyone is wrong here. Everyone so far has been pretty insightful. I've had a 30x40 lightjet print done from a 5 megapixel image, which consistently manages to impress people... sure, it certainly has its technical limits, coming from a 5 megapixel source file... but it looks damn fine. If you want to make a big print, and you think your subject warrants it... do it!
One of the most important factors in making good enlargements is meticulous noise removal, using the best interpolation software available, and applying the optimum amount of sharpening with introducing little or no extra noise in the process. Just because you've seen a sub-par enlargement somewhere doesn't mean that it's technologically unattainable to produce a good print from a "low megapixel" file. Good ideas are sometimes executed badly. In short, good enlargements come from well-shot photos, shooting in RAW, efficient noise removal, good interpolation (such as Benvista Photozoom Professional), and applying the right amount of sharpening (PK Sharpener).
I believe all current DSLRs will make great enlargements. But one of the biggest factors isn't the amount of megapixels, but how skillfully you process the files. But... more megapixels will obviously give you more fine details.