CPU cache / TLB effects? Using more address space isn't completely free.
In the case of Solaris I think there is much less of a chance of TLB effects?
For example on Solaris java automatically uses large pages (unlike Linux, Windows etc).
For, like, 13Gb of memory-mapped index, I've seen no noticeable difference between having large pages on and off under Linux. That's some anecdotal evidence, as I'ven't done any extensive research, but still.