I have not had any experience with them.
Toyo's web site says that they do produce the Proxes 4 Plus in a 245/45R19, but the online dealers I've looked at don't have it. Most of the reviews on Toyo's web site for this tire are pretty good, but there's 20% of them that didn't like the tire -- either poor handling, noise, tire failure, or low tread life.
TIreRack.com has very little information on the Toyo tires, they apparently do not sell very many of them. One concrete piece of information I found was that TireRack did test Toyo's max performance summer tire, the Proxes 1, against 3 other max performance summer tires, the Michelin Pilot Super Sport, Goodyear Eagle F1 Asymmetric 2, and the Bridgestone Potenza S-04 Pole Position. The Toyo came in
dead last.
Now, that was the Proxes 1, a max performance summer tire, whereas you're interested in the Proxes 4 Plus, an ultra high performance all-season. It's possible that the Proxes 4 Plus may perform better against others in it's category, but the performance of the Proxes 1 doesn't instill a lot of confidence.