On grass? Consider slightly bigger size!
If you fly on grass a lot, you will love the benefit of slightly bigger tires.
The 380-150-5 is about an inch bigger in diameter than a 500-5 and about a half inch wider.
It is also called a 15/600-5. Sometimes you see both listed with different prices, which I don't understand because they are essentially the same size.
Do a search on VAF archives for that size and you will find lots of discussion, including the minor mods to wheel pants to fit.
I find in soft dirt, sandy dirt, and on grass, they just feel so much better.