Get the biggest engine you can. That would be the 8.1 up to 2010 and then the Ilmor 6.2 or Indmar 6.2 SC in 2011. The 6.0 from Indmar will work but you will have to find the right prop for your activities and being at high altitude. It might not be enough if you sack it out for surfing.
I would also recommend having your wife ski both boats before buying. I haven't skied the 35 but the 45 is doable but she should try it first. Wake plate at 75-80% and 15' off works. Just make sure you are on edge across the wake.
2008 X-45 Pro Tour Red and White