@Chris Hill mathematically it would be faster to pay off 10k per month than save up 120k/year and throw it at the loan at the end of the year.

I definitely wouldn't recommend this as you increase the risk of your HELOC lender eventually freezing your account, plus I can't see mathematically how you are saving extra money this route as the only savings that I can tell are from shielding the HELOC interest payments by keeping the balance at $0 (or lower than it naturally would be for those withdrawing more than their monthly expenses).

One of the absolute best mathematical models for building wealth.

I am a former NASA robotics scientist, degreed in Applied mathematics, Aerospace Engineering, Mechanical engineering, (and a few other degrees not relevant in this case). this doesn't mean that I am automatically right and you are wrong.

You are the one failing to supply the mathematical calculations of how you plan to replace $8,000 a month in appreciation. 

My feeling is that if a finance whiz did a mathematical model on these approaches you would come out ahead focusing on one specific property at a time for early paydown but I am not that whiz so I won't undertake to prove it with math.  

My question to Mike is purely mathematical: how much market must loose in order for me to start losing money from my paycheck?

Strengths:  People skills, carpentry, gifted (IQ), career is math teacher, love analyzing deals, pretty good instincts with numbers, etc, lots of experience flipping home owner houses (hired by others to renovate bathrooms, kitchens, and have done whole house gut renos), degree in mathematics and interior design, basically skilled at making profit for not a lot of $$, knows what neighborhood I want to buyWeakness:  not a lot in savings, not clear judgement who is a good lender or agent (easily ‘fooled’), credit isn’t strong either because I just went through a divorceWhat do you suggest?  

Why do we make students take advanced mathematics past basic arithmetic?  

It may seem that it would make no mathematical difference whether it's deducted from one property or spread between the two of them, and often it does not.