Since you already ran a 5K I would use the average HR as your LT and set your zones using Friel's heart rate zones.

From http://home.trainingpeaks.com/...ide-to-setting-zones

It says to use the last 20 min of a all out 30 min run but I've found that a hard 5K is close enough.

Run Zones
Zone 1 Less than 85% of LTHR
Zone 2 85% to 89% of LTHR
Zone 3 90% to 94% of LTHR
Zone 4 95% to 99% of LTHR
Zone 5a 100% to 102% of LTHR
Zone 5b 103% to 106% of LTHR
Zone 5c More than 106% of LTHR

Read this book - Total Heart Rate Training by Joe Friel.

I would use both, actually. Use the Karvonen formula (% of HRR not purely from max HR) to estimate the zones and then validate them by checking where your 5K average HR falls in.
Here's a calculator Heart Rate Zone Calculator | The Athlete Blog

Karvonen formula uses heart rate reserve which better controls for an individual's fitness condition than pure % of max HR. So, at the same max HR (let's say 190) for someone who has a resting heart rate of 42 zones will be lower than for someone who has 60 (by at least 5bpm) - top end of Zone 2 146 vs 151. Once you calculate the zones, check where your average 5K heart rate (all-out effort) falls in. If it's in the upper Zone 4/lower Zone 5, you'll know that your zones are correct.

For a better estimation I'd add 5bpm to the max heart rate obtained from the 5k (or any other max HR test) as an additional adjustment. Often heart rate during a test is suppressed because of fatigue or lack of experience with HIIT - the body will not allow to go to the absolute limit.

Here's a good article on various max HR tests https://theathleteblog.com/...-maximum-heart-rate/

Not a direct answer but feel it's worth saying - Heart rate zones are not hard lines between zones, but general fuzzy areas. There's very little difference physically between the bottom of Z3 and the top of Z2. It's almost better to think of zones as a central target, Z1 is 125, Z2 is 132, Z3 is 140, etc.

The difference in individual variance is also going to overshadow the difference between models. Usain Bolt and Eliud Kipchoge go for a run together at 90% of LTHR. Imagining that they go at the same speed, do we really believe that run will have the same training stress on both of them? Kipchoge is going to be at a very high % of his VO2max, Bolt is going to be far far lower VO2max%.

At the risk of going completely off topic, I don't see a lot of value in the 5/7 zone model. The 3-zone model is where Z1 is below ~LT2/VT/conversation threshold) Z2 is below lactate threshold, and Z3 is above. This pretty much captures the physiological lines, as far as they exist.

I let my 955 do the calculations for me, and I've noticed that Max and LT keep getting adjusted after hard workouts. Not by a lot, but they do change, which makes me think that heart rate zones are a mystical construct to confuse the masses.

I like your screen name, BTW. I have a BS in Applied Mathematics. (But I use it to pretend to be an engineer) : )

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"...the street finds its own uses for things"

I'll leave zones to others, but.
Not clear (to me) how you established your HRmax from running a 5k. Quite useful to establish it without relying on extrapolation or other formula, as well as a reliable RHR (taken in the morning on waking, with care).

Best way to establish your actual HRmax is to warm up well arriving at the bottom of a gentle hill at least a mile long. Start up at a good pace and gradually increase till sprinting at the top (ideal if the hill turns up slightly for that final bit). Key is that you are almost but not quite spent (as HR will drop when fatigue slows effort).

I certainly favour zones based on range (ie your HRR).
HTH

The OP hasn't logged in November of 2016.

Hopefully they've figured it out by now.