GDMBR - start in Banff, better in June or July

I'll be starting in Banff sometime this summer to ride ~2,000 miles of the GDMBR southbound. 18 days available to ride, ~100-120 miles/day.

Constraints:
- Can't be in Banff until June 17th
- Need to be in Portland on July 9th

Two potential time slots:
1) June 17th-July 8th
2) July 11th - July 31st

I understand that the later date results in less snow to push over up north, but would the heat in southern CO be significantly worse a in late July vs. early July? Not as concerned with rain/mud/temps/fires in NM as I don't plan on spending much time there.

The later date is preferable for my wife's sake (she'll actually be driving my bike out to Banff and having her own vacation down the Rockies in a car) - I'd actually prefer a bit cooler weather, but I'm fine to 90 degrees or so.

Would leaving on the later date be significantly worse in terms of storms/fires/etc in Wyoming/Colorado? My knowledge at this point is that I'll be fine and it's really only NM that should be avoided past mid-July...I'm just trying to confirm that understanding.

I tried to search, but wasn't finding the information I was looking for....if there's a place that I could dig into this myself, feel free to point me in that direction.