I'll ask my wife tomorrow and she'll contradict whatever I suggest BUT they are all lovely and scenic and not overly terrible to drive. I suspect that its is likely that by far the greatest danger to your likelihood of lifelong happiness will occur at the conference :-). Almost a 3 side coin toss - but I'd say take the most northerly. But all are marvellous.
I'd recommend taking the MOST scenic route as it sounds like you are not getting much opportunity to see the country otherwise - although Queenstown itself is quite picturesque and nicely surrounded by mountains which loom over the town, usually almost unseen by locals who get used to them. The two most northerly routes work out at just over 80 kph average on Gargoyle's route finder and the southern one is a few kph slower - although I'm not sure why. I'd drive any of them without any concern at all. At Google's suggested trip times they should be a comfortable drive. Add 30 minutes to any one and it would be a very sedate drive
All routes involve some winding road - this IS NZ after all.
I would not have thought of wind as an especial hazard anywhere there - the most dangerous place for that that I've met in NZ is the Auckland harbour bridge - not a problem for you on this journey. That said, you can find the occasional wind blown cutting essentially anywhere in NZ and its just one of the things to be aware of - but no more so than realising there MAY be 500 sheep on the road just around the corner or remembering that hammering into blind tight corners is more likely to reveal yet another even tighter corner than in some other countries. BUT anything like sensible driving will get you there safely. I've read comments by Australians noting our lack of signage but that is hard to understand - all highway corners of any risk at all are well posted with advisory speed signs which are generally VERY conservative. You can probably always take them in the wet at above posted speed. (With an old style Supercharged MR2 in the dry you can double them with ease at up to the max speed I was willing to drive - and triple the slower ones with 'a little concern that you may just possibly have overdone it this time' - but you never had.)
Almost not related: On the top two routes you pass the Southern end of The Crown Range on your final leg. You don't get to drive it unless you want to - and you don't :-). When it was gravel it was quite something, but those days have gone, alas.
Red Bull quad rotor RX7 does the Crown Range - it's hard to tell whether the chopper pilot or the RX7ian are having the most fun.