To follow on what John has just said, if you do keep your T3, you can also download most of the KN7000 styles that have been converted to play on the T3 from the following site:-www.psrtutorial.com
I had most of the KN7 styles on my T3 and I saved them to my PC before px for a T4. These are now on the Tyros 4. In fact, some clever people on the psr site, are already converting styles to play on the T4.
They also offer conversions for most other keyboards, such as Roland, Korg, Ketron and earlier Yamaha keyboards.
A Tip: if you do transfer styles to the T3, open up all relevant Folders beforehand to see whether there are any hidden folders. I made this mistake the first time I did this, I just copied and pasted the Folders across thinking all files were going with them only to find that some of the Folders had other Folders and Files inside them, so of course, when I opened the first Folder, it was empty. Like I've said many times before, I really hate the Yamaha operating system and can't wait for some enterprising keyboard manufacturer to come up with an OS similar to the Technics, it is so simple to use and quick to load.