Training & Nutrition - Heart rate monitor versus cycle computer

I have a Timex HRM that I've been using for a while and I just re-installed a Cateye cycle computer on my bike. Just a few facts about me. I just turned 42, used to bike a lot but not so much in the last 10+ years, weigh about 190 but hoping to get back down to 170. I really just got back into cycling regularly in just the last month and change. I set myself a goal to train enough to ride my first century on September 18. So, here's my question.

My HRM is set right now for a basic cardio training zone of 130 - 148 bpm (my max HR is 186 bpm). I find that I tend (lately) to ride a bit out of the zone. Usually I stray out of the upper end of the zone to the tune of 150 to occasionally as much as 170 bpm. What I found with putting the cycle computer into operation is that my favored pace tends to be about 14-16 mph, which often puts me out of the zone. I've been thinking about just setting the upper range of my training zone a bit higher.

I'm going to buy a Cateye Astrale to replace my Enduro 8 so that I'll have the cadence feature to help me figure things out. I'm wondering if I should just set the HRM higher and train more in the zone, speed-wise that seems to be more comfortable to me. What do you all think? I really think the best feature of the HRM other than making sure I don't kill myself but exploding my heart, is the calories burned estimation. I guess I'm just trying to get a handle on how to use the different technological gadgets to help me train to best effect. Suggestions?

You can't kill yourself by exploding your heart (unless you have heart defect). The body has a host of fail-safes to prevent that. If it was possible then every 45+ and 55+ masters race would have a caravan of ambulances and hearses trailing the peloton.

If you go as hard as you can, then harder, then sprint, you'll see your max HR. You might puke or get dizzy but that's about the worst that can happen.

HRM calories estimates are almost always high, sometimes by as much as double what the real value is. You can use them for comparison purposes (i.e. to get an idea if the total training load for one ride was lower or higher than another) but don't use it for diet purposes.

An HRM can be useful for pacing yourself, especially if you're riding your first century. But keeping to your "zone" in training is just training yourself to go slow. Try going by how you feel rather than the HRM. Figure out what pace you can handle for different lengths of time and then use that to set a limit for the beginning part of the century. I see a lot of new century riders treating it like a race at the beginning and then finishing poorly if at all. Start out easy so you can finish strong.

If you feel comfortable at a higher heart rate then that's a good thing as far as I can see. You will burn more calories and get your heart in shape.