To Simon's comment about using Kents as rootstock, I started a few dozen Kent seedlings last year for that purpose. It might be my particular climate/location here in Florida, but nearly all of them had major issues. They started out gangbusters; strong, thick rootstocks that I could graft onto nearly immediately. I had late season takes last year on them with Pim Sen Mung, Honeykiss, Neelam, Sweet Tart and a few others. PSM and Honeykiss went to flower over the winter; I followed a recommended removal procedure of letting a few pea-sized mangoes form while removing the rest, but I couldn't stop them from flowering. Come spring, they both were having growth issues; constant new growth below the graft that I had to remove, while above would develop new growth spikes that never did anything. Union was solid and I tried repotting both, but they slowly died above the graft line. The others all had growth issues, none so bad as those two, but so bad that I've been reclaiming the scions to graft onto different rootstock. Anthracnose ravaged the trunks of a few of them all season long. It was a bit of a horror show.
Might have all been some mistake(s) on my part, but I started zero Kent seedlings this year. I really like the fruit and how late it is (many trees around here are still holding), but no more grafting onto them for me.