To save group price for the products, the following works for me.
$product->setData('group_price', $group_pricing_data); $product->save();
However, it takes a while for mass updating products. The faster way to save only attributes via saveAttribute() does not seem to work on group price.
$product->setData('group_price', $group_pricing_data); $product->getResource()->saveAttribute($product, 'group_price');
Is it because group_price is not EAV like the other attributes, and if so, is there any other way to just save only group pricing?