Version of Kotlin plugin for Gradle plugin

I’m writing a Gradle plugin in Kotlin.

My plugin also has a compileOnly dependency on kotlin("gradle-plugin"), since, if and only if any project that applies my plugin also applies the Kotlin plugin, my plugin will modify KotlinCompile tasks. (I need to investigate optional dependencies to see if something is better for this than a compileOnly dependency)

I’m building my plugin with Gradle 6.0, which has Kotlin 1.3.50 bundled.

Kotlin 1.3.60 was just released.

My plugin should be made to work for older versions of Gradle, too.

What version of the Kotlin plugin for Gradle should I apply, and what version of kotlin("gradle-plugin") should I depend on?