Ton37 makes an excellent point. The Genos has a lot of things on it you may never use. The SX900 has the same sound engine and most of the same styles and voices.
Leading Edge says that customers won't likely hear a huge difference, which I agree with to a point. You are largely a home player, so you will hear the difference. Either way you go, make sure you own quality speakers. Some claim the Yamaha speakers are great while others say they're overpriced for what they are. Perhaps you already have that base covered with your T4.
Were I to criticize the Genos, it would be in the upper surface quality. It displays dust and fingerprints very easily. The display doesn't tilt and there's no contrast adjustment, which makes seeing the display difficult under certain lighting conditions. Then again, if you're always at home, you can light the room to compensate.
The key action is far better than the Tyros series. The pianos are much better but have a long way to go. Yamaha needs to take a lesson from Nord and dedicate a few GB to just the pianos. Then, they'd have a killer piano sound.