I skied on my IM 77's last year for the full utah gathering, we had a few fresh powder days, i'm a decent skier and not totally unfamiliar with powder and managed just fine. Where I teach this year, most days I'm on my Head Johnny 94's but, you will find me on my IM 77's now and then, and occasionally get caught having to take them up top in the powder (i was teaching edgingtechniques on groomers and then went for a free run, mis judged conditions three days after a snow fall, etc) and still manage fine, with proper technique. But life is much more fun in powder on a powder ski. I also taught a how to ski powder lesson this week on my IM 77's....Why?, bEcause the lady requesting me for the lesson had on 80 underfoot and it only seemed fair I not overly challenge her but making sure, with the same under foot, I'd have the same handicap as her. I did suggest she look for a powder ski to use for powder days now that she was enjoying more powder days and wanting to get better in it. I was also working a fair bit on groomers with her before the powder to improve her base technique as part of improving her powder technique.
All that said, i'm female and 5' 5" , 140 lbs and get some float with my 77 underfoot and widish tips. If you are 200 lbs you won't get any float at all. You are not guaranteed powder days for your entire trip either. You may find you can use your tiger shark just fine and rent a ski one or two days if you get a good powder dump.
As far as buying and reselling skis, you're much wiser to rent at the hill. you'll not have the worry of reselling them. At this time of year you may end up holding on to the new ski. So unless you really want the other ski and wouldn't mind ending up stuck with it for the times you get powder, just rent when and if you get a powder dump of more then a foot while you are away.