I really think it'll just come down to the national environment in the end, and that's what's annoying since that can be somewhat hard to predict.
For example, key 2014 Senate races were expected to be much closer than they were. Will we see the reverse? Will the wave be equalized by unexpected Republican turnout?
Now, I doubt Cruz will lose, but I could see him winning from anything from +10 to +2 (maybe even +1) based on the national environment.
Same in thinking Cruz will win, but I think it'll be more of a turnout game than not. GOP still has more people turning out than Dems even in the primaries -- and Dems had WAY more going on then. The Beto campaign is going to have to pull off some sort of turnout miracle in the persuadable suburbs and with the Latino community to get close to Cruz