We have the designer vinyl and it can get that hot in certain conditions so we're glad we have snap in carpeting too (even that can get pretty warm though). However, without being able to compare directly side by side, it seemed like the platinum seagrass and some of the teaks were even hotter than the designer vinyl so glad we have what we do.
The new bamboo or cream colored seagrass could be cooler but wouldn't have worked with our color combination. And as indicated, I think they all get hot to an extent, and definitely if you are in a place like AZ. If you really concerned about it, you may want to consider carpet which, as indicated, still can get quite warm but is still quite cooler than our vinyl. Since many wouldn't think about carpet on a boat anymore, I think the vinyl with snap out carpet is the best of both worlds if you can afford it.