[R] Windows 2x faster than linux x86_64?

[thomas.davidoff at sauder.ubc.ca]

I did a speed test with a colleague.  We basically have identical Lenovo
ThinkCentres.  He has 8 vs my 4 G RAM, but I don't think that's the
issue.

code:
length <- 2*10^6
a <- runif(length)
b <- runif(length)
print(summary(lm(a~b)))

Running Arch x86_64 this takes about 16 to 17 seconds.  I *think* I have
compiled arch=i686  and arch=x86_64 with little speed difference.

On windows, this takes 7 to 8 seconds.

Thoughts?