XID wraparound metrics are unclear
So, the xidWarnLimit is 3.747 billon where my current txid_current>70 billion. And strange thing is txid_current is greater than xidWrapLimit which is 3.758 billon.


You are presumably looking at the raw return of txid_current(), which is not a 32-bit value like the XID Limits you are looking at. Instead, it is 


  a 64-bit format that is extended with an "epoch" counter so it will not wrap around during the life of an installation.


(ref). You can coax a 32-bit value out of txid_current() which you can compare against your xidWrapLimit, xidStopLimit, etc. like this:

SELECT txid_current() % (2^32)::bigint;


H/T to Erwin for this tip. Remember that these XID values wrap around at 2^32.

For what it's worth, I think that blog post you linked to is excessively complicating this topic. To watch out for XID wraparound, you really just need to check:

SELECT max(age(datfrozenxid)) FROM pg_database;


and raise an alarm if that max. age is over 1 Billion or so. And if it gets close to 2 Billion you are in imminent danger! You can use a tool like check_postgres.pl which will handle this check for you with some configurable thresholds.