For James' benefit... been over this with Bigtime in detail over the last six weeks or so...
Mine suffered the exact same issue, the only symptoms being missfire once warm (0300 0306 always, other cylinders if left idling for any time once missing started) and coil 6 showing 40kv against 60kv for other 5 cylinders (tested with three different coil packs from other working cars at the 2011 Lakes meet by a very patient MarksDTM... same result each time... pot 6 was 20kv light)
Bigtime has investigated the issue far more scientifically than my efforts but has changed the same components in a similar order
FWIW mine was cured with a new (sh) loom, although this took two goes
New coil packs, plugs and known good injectors and ecu all made no difference, which only left the loom. First loom was better, but still played up occasionally, second loom resolved it.
Might be worth acquiring the loom from Robsey MV6s breaker if it's still available... 3.2 auto, with about 45k iirc