I own the original QuickSilver refill. Is there any extra on the Core version?

Yes, but you don't need to pay for it. There are some extra patches on the Core version. You can download them as an update for free. See the html manual on your QuickSilver CD ROM on how to get them.

What's the advantages of the Core version compared to the original QuickSilver CD ROM release?

On the one hand, the price. You can get the Core version for less than half of the price of the original QuickSilver, and moreover there is no postal fee.
On the other hand, you don't have to wait for shipping, but after purchasing you can download the stuff immediately.
And last but not least, if you change your mind afterwards and want the original CD ROM version as well, you can purchase it for a special upgrade price. The upgrade costs 25 Euros only (instead of 45).

How long does it take to download?

It depends on your connection's speed only.
The file is provided by the very fast secure servers of share-it. If you have a cable/T1/DSL connection, the download time is less than 15 minutes. If you use an 56k modem, it takes about 140 minutes.

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