Welcome [member=66576]memilanuk[/member]
Generally, the extractors offer the same performance, except for the ultra small CT SYS. As Alex mentioned, the biggest difference is capacity (and consequentially weight). The other difference are accessory compatibility - Bluetooth remote trigger, the new cyclone and the boom arm set up, which are only compatible with the CT26, 36, 46. The Bluetooth is really handy if you’re doing shop or site clean up as you work! Note: Festool is releasing new midi and mini models in Europe with Bluetooth built in. Those won’t see North America for a year give or take (Festool hasn’t said when).
Also note, if you’re in North America, you get 10% off with the purchase of a tool!