I touched on my experience with mostly butter, but some cream, elevating my LDL-C here:
I jolted awake last night thinking about familial hypercholesterolemia (seriously). Heterozygous FH usually results in a total cholesterol of around 300 mg/dl (and an increased rate of heart attack). Homozygous FH usually results in a TC of around 680 mg/dl (and death during childhood). FH reduces cholesterol clearance in the blood because some portion of LDL receptors are absent, so the LDL molecules aren't able to bind and unload their cholesterol cargo. This is important because the LDL-C oxidizes over time (creating oxLDL) which is taken up by macrophages which then become foam cells. They can then be trapped in blood vessel walls and contribute to the formation of plaques.
There's something about the ratio of myristic, palmitic and lauric acids in butter and cream that makes it the most potent dietary way to downregulate the hepatic LDL receptors. It happens to some extent with coconut oil, but I've seen studies that showed it to be about half as potent as butter. I don't believe that it is a systemic clearance issue like it is with FH, but rather just focused on the liver and its ability to clear excess LDL-C from the circulation. I've never seen any evidence for this, but my assumption is that the reason hepatic LDLR activity is downregulated with these fatty acids is that more LDL-C is needed in circulation during the rapid brain development of a nursing neonate. Any dairy would likely have this effect to some extent, but a highly concentrated form of cow's butter is a strongly exaggerated dose of these fatty acids, which in this case have a drug-like effect on cholesterol clearance.
As serum cholesterol levels increase, there should be a negative feedback mechanism that reduces and probably eventually nearly halts endogenous production of cholesterol. The cholesterol that builds up in the bloodstream is likely dietary cholesterol that slowly accumulates in LDL molecules.
I had only been eating a lot of butter for a few months before I hit a TC of 391. I have no reason to believe that going longer wouldn't have increased it even further. I know I don't have FH because lipid panels before that one have not had a TC that exceeded 168. This didn't occur during a time when I could create vitamin D via UVB and cholesterol, so that's a factor as well. Indeed, there are many people eating a paleo-ish diet high in butter/cream who have reported very high LDL-C levels. Take a gander at this one from PH: http://paleohacks.com/questions/3906/very-high-total-cholesterol#axzz1X1hEFAqS
I don't know exactly what she was eating but she says very high fat and that she eats dairy and 550 mg/dl is no joke. I would advise someone with a TC in the 400+ range to immediately stop eating any dietary cholesterol, go low fat, get out in the sun and try to maximize serum cholesterol clearance ASAP. Mine dropped by 20-something percent in about 5-6 weeks without sun, and is likely in the 200s right now. However, I certainly would not give the same advice to someone with a healthy level of cholesterol (low to mid 200s) like our misguided doctors do.
In the same way that having elevated levels of triglycerides in chylomicrons or VLDL floating around our blood is dangerous, I'm fairly confident that there's a safe range for LDL-C and that it being "big and fluffy" does little to make the situation safer. It is highly unsophisticated to think of LDL-C as "bad cholesterol" since it's necessary for our survival, however at these inflated levels (for which I'm sure we have no evolutionary precedent) I think it could contribute to atherosclerosis. I think that a heavy butter/cream intake simulates FH and could cause the same results.
At the very least, we might replace the butter and cream in our diets with coconut oil and have the added benefit of reduced lipogenesis due to the much greater amount of MCTs.