textdumps are too slow

I have servers with lots of RAM yet slow swap disks.  So full crash
dumps are too slow.  Instead, I use textdumps, which are theoretically
much faster.  However, these servers also have about 10,000 threads
apiece, so textdumps are also slow.  They take tens of minutes.  I
have dual console setup: both serial and video.  It seems to me that
the speed of the textdump might be limited by the video system.  So is
there anyway to capture a textdump without printing everything to the
console?  textdump(4) implies that there isn't; you must print stuff
to console in order to capture it, and you must capture in order to
dump.  Would somebody please tell me that I'm wrong?

-Alan