Ion torrent appears to be the same platform as 454, but with detection via chemical means (ISFETs) rather than optical transduction. One of the big drawbacks of the 454 technology that doesn't get talked about a lot is that the immulsion PCR/microbeads require a lot of preparation before the actual sequencing run. On the 454, I believe the sequencing time was ~8hrs, but the preparation time (at least at the facility where I was involved) typically took more than 8 hrs. In terms of actual sequencing time, it's the best system. But as you said, read length is a major issue with all of the current "nextgen" systems that should be resolved with nanopore sequencing.