I have 2 Hondas and 1 Toyota. Like you, I am interested in the correct oil weight for them. I live in Tennessee so my climate is more moderate than South Texas. After reading numerous posts on BITOG, and considering my family's short-trip driving style, I decided that the best thing is to go for a 5W oil for fastest pump-up on start-up. However, also considering high-temp oil breakdown issues (my '97 Toyota is one of the so-called "sludge motors"), I decided to switch to synthetic M1 5W-30. As I understand it, Synth flows even faster than Dino, and has good high-temp and low-temp stability compared to Dino. This seems like a good choice for all of my cars, even though my newest Honda specifies 5W-20.
I am still in the process of switching to M1 (2 of 3 cars switched), but I have already noticed that they run a little quieter at idle, and seem to rev quieter and smoother.
I really don't know anything about oil viscosity selections, and have not really learned much on BITOG because of the great passion / opinion on oil thickness. Somebody told me 20 years ago that FILM STRENGTH is what you really need and film strength can be somewhat independent of viscosity.
For me, with a lot of stop-and-go driving, I decided that I do not want a thick oil that prohibits the engine from reving freely. Again, M1 seemed to me to be a good choice.
The cost of Synth is a serious factor(!), but I think is worth your second consideration. You really do not want to risk thermal breakdown of your oil, as I have, and I do not think that a heavier oil always has a higher thermal breakdown than a thinner oil. This is my opinion only.
Best Wishes as you motor along!
SWS