Maffetone vs Van Aacken vs Lydiard

I've been running mostly aerobic for the past 12+ months. I keep my heart rate monitor on and it beeps when I exceed a certain level. Usually, that level has been around 150 or less. It's based on a combination of Lydiard, Maffetone, and Van Aacken. Actually, I guess it's really the Van Aacken standard credo of not to exceed 150. But it matches with the easy aerobic Lydiard zone too and is slightly higher than the Maffetone cut-off. Here are those different guidelines:

Maffetone = 180-age (with a slight adjustment based on past run history)
= 180 - 46 + 5 = 139
Zone = 129-139

Van Aacken = 150
Zone = 135-150

Lydiard "easy aerobic" = 60%-75% Heart Rate Reserve (HRR)
% HRR = % (Max HR-Rest HR) + Rest HR
[My MaxHR=190, RestHR=50]
Zone = 134-155

When I analyze most of my running over the past year, it has been mostly Maffetone aerobic (below 140). I rarely hit that 150 "HR beeping" barrier. To increase my current fitness, I need a change. I still will focus on primarily aerobic runs, but with a higher threshold. Plus, I'd like to mix in more variety. I'm swapping Maffetone and Van Aacken for Lydiard. By allowing a heart rate up to 155 for easy and long runs, I allow myself a quicker pace, but still will be running under control and primarily aerobic. The next Lydiard zone is "sub-threshold" (or marathon-pace) at a heart rate of 75-80% HRR (for me, 155-162). At a heart rate of around 163 (HRR of 80-85% or 162-169), I am heading into tempo-paced runs and my lactate threshold. Nothing wrong with this HR or pace, but I need to be prudent when venturing into this zone. For me as an ultrarunner, I don't think I need to exceed 169. Fast track intervals will possibly bring greater fitness, but at an extreme risk. I'd rather be conservative and stop at tempo runs. My basic winter training week will look like this:

MON: walk or rest
TUES: 7 @ 134-155
WED: 6 @ 155-162
THUR: 7 @ <135
FRI: walk or rest
SAT: 20 @ 134-155
SUN: 5 @ <135

I'd like to aim for 25-30 miles each weekend, split between Saturday and Sunday as necessary. Once spring comes, I'd like to add in tempo runs (HR=162-169).