Best size for image zoom / thumbnails?

[alitraeps]

Hi, what is the best size to make product images so that that 1) they look good in the zoom on a full-width single product page and 2) also look good as thumbnails?

Here is the shopping category page:

http://198.46.81.216/~yvelco5/product-category/almog-collection/

Here are two examples of products in that category:

Almog White Gold , Pearl & Diamond Ring

http://198.46.81.216/~yvelco5/shop/almog-white-gold-tahiti-pearl-diamond-ring/

On each product, the zoom seems to take a long time to load.

And then if you click the back arrow to go back to the shopping / category page, the thumbnail seems to be hyper sharpened, as if it’s loading the full-size image, but smaller.

Please advise what the best settings are for this.

Thanks.

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