I am staying in Tiberias (Israel) and have about one week to spent after New Year's Eve (Jan 6-13). I thought of heading south to Eilat by bus and then go to Dahab. My question: how about diving the wreck Thistlegorm and other dive sites: visibility, temperature (water), ...?
Thanks,
Wim

I don't think you'll be close enough to Thistlegorm from Dahab - it's a massive day trip from Sharm - usually done as a liveaborad out of Sharm
There are no wrecks in Dahab - you could settle for the Blue Hole
It's going to be chilly in the watwer and after diving.
There are trips to Thistlegorm from Dahab, but in January there will probably not be enough people around to get a trip together.

I'd go to Sharm and then try to find a trip.....Thistlegorm can be done as a day trip but is not cheap (and a long, long day). some operators (emperor etc) insist on a day's check out as well so you'd need a couple of days
Day boat diving out of Sharm is really good, and quite cheap if booked in advance (check out operator websites)