I would go for a high-speed USB solution with a buffer; but - and I stress it - I would be picky about the PC, its hardware/chipset/USB connectors and cabling, disk, OS, installed software (the less the better, bare OS is preferrable), strictly NO network (as Bob Marley (nearly) said: no network no cry). If you can, get somebody knowledgeable to purge the lots of unnecessary crap from Win/Lin, whatever you choose, which might influence the timing.

As far as particular chips, I'd go for the FTDI chips, as they have a record of decent driver support. They now have a new line of high-speed USB chips. Their xx245 chips have an 8-bit interface and a small FIFO, so basically you just watch an "can-write" handshake signal and if it indicates "green", you put data on bus and pull strobe. They indicated sustainable 1MByte/s flow on their "classic" line of chips (on unloaded USB line and PC etc.), so I believe they tried that. You might perhaps ask them about first-hand experience.

So, I would simply take a CPLD and a SRAM - say, half-a-megabyte, which are relatively cheap and easy to buy - build the deserialiser and FIFO address registers and the rather simple steering logic to the SRAM, add some clock, add the USB device, and it's roughly done.

JW

PS. What if some of the logs are missed/erratic, say, one in ten or so, but you have an indication that this happened? Could this be tolerated?