Redline oils (all, even the 5W-30) are 1,200 to 1,300 ZDDP. I left mine in for a year (1,800 miles) and the ZDDP level did not move. Redline also sells a ZDDP additive for about ten bucks. Using Redline and their additive I'm now at about 1,500 ZDDP.
Don't be using a really thick
oil just to get the higher ZDDP lever you're after.
High ZDDP levels in Mobil1 are very expensive.
Bob