Change from XTCModified to Magento - Rankings?

Hey guys,

I´m currently ranked very well with an XTCModified Shop but think about changing to Magento.

Of course I´m going to lose all rankings because the URLs will change from XTCModified to Magento, but how are my chances of ranking the new shop? Will Google pick the new URLs up quickly and rank me where I´ve been before or do I have to start all over again?

Does anyone have experience with this?

Thanks in advance, guys!

Can you not just build the pages on the same URL's? if not 301's will be your best bet.

But you are on your own, you could either lose them or go back to normal