I changed MHR to 198 on strava about a week ago or so.
It did't made any difference really - amount of time spent in Z4 remained about the same but with a lot less in Z5.
This whole Z5 thing made me worry as it was totally unrealistic.
Looked back in my very first Mt Diablo climbs and HR curve and numbers were about the same
Here's my first ever climb Bike Ride Profile | Mt Diablo for first time! near Danville | Times and Records | Strava - I only had bike with gears for about a month so the whole climbing thing was totally new to me, also I was quiet de-trained as I did not ride much and just recovered after injury.
2nd climb Bike Ride Profile | Mt Diablo. Made it all the way up without walking last 50 feet near Danville | Times and Records | Strava November 2, 2013
My fastest (early May) climb Bike Ride Profile | 5/10/14 Danville, CA. Diablo #39. All me this time - no wind at all. near Danville | Times and Records | Strava May 10, 2014 (5 months later).
HR graph on a very first ride is very uneven with some noticeable drops but if I compare 2nd ride and fastest (would be Mount Diablo climb #37 ) it is clear that shape is almost identical with latest one being a tag smoother.
The only dramatic difference is that power on 2nd ride was 184W vs 254W on fastest one (strava calcualted numbers).
That 70W resulted in 17min improvement from 1:19 to 1:02 which is ~20% improvement over 5 months.
I kind of doubt I'll be able to improve that much ever again but really hoping for 5 or may be 7% gains for next 5 months.