tmpfs can cope with huge amounts of data no problem.
BUT it *defaults* to "half available ram".
I got bitten by this when I put /var/tmp into tmpfs on gentoo, and then wondered why OpenOffice wouldn't compile :-)
I always set swap to (at least) twice available ram, which on my system is 32Gb (kernel 2.4 proved that the "twice ram" rule was NOT obsolete, and nobody has yet given me any reason to believe things have changed since then).
I think my tmpfs partitions are all set to about 10-16Gb in size. They're all fine. If you use enough space on the partition, it will simply spill into swap.