I can't say for certain what those upgraded transformers have done for the sound. However, from my experience with other amps, upgrading the power supply is usually one of the more noticeable upgrades that you can make. That plus transformers start to get quite expensive once you start climbing up. If you're spending money upgrading components, that's where I would expect a good chunk of it to go.
That all said, if shipping is of such concern to you and this amp is a significant expenditure for you... are you sure it's the right choice for you? Where are you located? What other options have you looked at?