we have a four hour connection time in BKK and since it is on a new PNR the departure tax is paid for. Looks like it might be best to go through immigration in bKK, pickup bags and re-check in. Sometimes BKK is quite slow with immigration whereas other times its quite fast but seeing as we have a large window I dont foresee problems. TK68 from IST to BKK seems to be delayed by 30-75 minutes usually but this still leave ample time!