Bootstrapped CAC and LTV math in 2019

Bootstrapped CPC rule of thumb: MRR/25

I'm doing some financial modeling and found Jason Cohen's article from 2013 https://blog.asmartbear.com/bootstrapped-cpc.html in which he gives two rules of thumb for bootstrapped businesses:

LTV = MRR x 20
and
CAC = LTV / 5 as a spending cap

which produces

CAC = MRR x 4

He then goes on to suggest an average conversion rate of 1% is typical for SAAS businesses and you shouldn't plan on higher.

As that was five years ago, does anyone have a feel for how those figures may have changed, if at all?

Note that his emphasis on strictly limiting spend on CAC for bootstrapped business is because they can't afford to deeply over-spend to build volume, unlike funded ones.