I have not even decided if I want to undertake a kernel build, but for the sake of discussion, if everything happens to be in the stock kernel, why, other than file bloat, would you want to build a custom kernel? In FreeBSD, you can remove all those devices and drivers that are not needed, and, depending on how much stuff you add or delete, can make a decent size reduction in the kernel itself. I'm not smart enough to know if there is a performance trade-off with a whole bunch of unneeded modules or drivers in the kernel, but perhaps common sense tells me that there must be some kind of performance hit otherwise. Kernel building in Linux is very much different from the BSD camps, and I'll admit I'm not sure I understand enough about the Linux build process to undertake it.
Comments appreciated......