Copying the playground example here as they will be deleted:

app.html:

<template>
    <lightning-button label="Load" onclick={load}>
    </lightning-button>
    <lightning-button label="Test Main" onclick={test}>
    </lightning-button>

    <c-performance-child1 myarray={myarray}></c-performance-child1>
</template>

app.js:

import PerformanceInherit from 'c/performanceInherit';

export default class App extends PerformanceInherit { }

performanceInherit.js:

import { LightningElement, track, api } from 'lwc';

export default class PerformanceInherit extends LightningElement {
    compId = 'parent';

    @api myarray = [];

    load() {
        let myarray = [];
        for (let i = 1; i < 111; i++) {
            myarray.push('elem ' + i);
        }
        this.myarray = myarray;
    }

    test() {
        let t1 = new Date().getTime();
        this.myarray.find(item => false);
        let t2 = new Date().getTime();
        console.log('find ______', this.compId + ' => ', (t2 - t1) + ' ms');

        let t3 = new Date().getTime();
        this.myarray.forEach(item => item);
        let t4 = new Date().getTime();
        console.log('forEach ___', this.compId + ' => ', (t4 - t3) + ' ms');

        let t5 = new Date().getTime();
        this.myarray.filter(item => false);
        let t6 = new Date().getTime();
        console.log('filter ____', this.compId + ' => ', (t6 - t5) + ' ms');

        let t7 = new Date().getTime();
        this.myarray.map(item => item);
        let t8 = new Date().getTime();
        console.log('map _______', this.compId + ' => ', (t8 - t7) + ' ms');

        let t9 = new Date().getTime();
        this.myarray.findIndex(item => false);
        let t10 = new Date().getTime();
        console.log('findIndex _', this.compId + ' => ', (t10 - t9) + ' ms');

        console.log('_________________', this.myarray.length);
    }
}

performanceChild1.html

<template>
    <lightning-button label="Test Parent"
                      onclick={test}>
    </lightning-button>

    <c-performance-child2 myarray={myarray}></c-performance-child2>
</template>

performanceChild1.js

import PerformanceInherit from 'c/performanceInherit';

export default class PerformanceChild1 extends PerformanceInherit { }

performanceChild2.html

<template>
    <lightning-button label="Test Child"
                      onclick={test}>
    </lightning-button>

    <c-performance-child3 myarray={myarray}></c-performance-child3>
</template>

performanceChild2.js

import PerformanceInherit from 'c/performanceInherit';

export default class PerformanceChild2 extends PerformanceInherit {
    constructor() {
        super();
        this.compId = 'child';
    }
}

performanceChild3.html

<template>
    <lightning-button label="Test Grand-Child"
                      onclick={test}>
    </lightning-button>
</template>

performanceChild3.js

import PerformanceInherit from 'c/performanceInherit';

export default class PerformanceChild3 extends PerformanceInherit {
    constructor() {
        super();
        this.compId = 'grand-child';
    }
}