I think RAM would affect reads more than writes since RAM is primarily used for caching reads. Plus as I said earlier, I have 8GB RAM (plus likely a whole lot more running on my box than lowfat since I run about half a dozen VMs on there as well) and I have faster writes.
The only ZFS that comes to mind which could be affecting his RAM requirements would be if he has deduping enabled - but I really wouldn't recommend that on his CPU specs either.
re the ZIL drive, it's not recommended running a lone ZIL drive like that anyway. Since ZIL is used as a ZFS log table, it should be mirrored as if the ZIL drive goes down then you can lose data (and given how robust ZFS is, running an unmirrored ZIL drive feels a little like intentionally breaking the file system). Obviously this is just personal use so the lowfat is free to build the system as he chooses, but I wouldn't be happy with that in my own set up (in fact the problem of paring SSDs is why I didn't bother with ZIL on my own ZFS storage array)