Ok, so here are my initial thoughts:
1) Both the Takatsuki 274B and the KR-Audio 5U4G Riccardo Kron Anniversary Edition are DEAD QUIET. In my Woo's, both at full crank produce NO NOISE WHATSOEVER.
2) The Takatsuki 274B is the leaner and cleaner of the two. It's probably faster, more precise, and more spacious. The soundstage is wide open, everything is exactly where it should be. It is VERY clean sounding, meaning it doesn't really add much warmth to the sound. Plenty of energy, speed, and breath. It does not suffer from tube sag when pushed.
3) The KR-Audio 5U4G Riccardo Kron Anniversary Edition is the beefier, heavier-hitting of the two. If you want that warm, rich "tubey" sound, this is the one you want. Plenty fast, plenty of energy, but a touch slower than the Takatsuki. It is MUCH heavier sounding though, so bass and sub-bass are more rich and lush. It is not as precise as the Takatsuki, though, so there's less air or soundstage.
Avenge Sevenfold's cover of Pink Floyd's "Wish You Were Here" is an excellent example of space and separation. The opening guitars are resolved quite clearly by both tubes. With the RK KR, you get more of that tube amp sound, whereas with the Takatsuki you get more detail. The kick drum is more impactful and the cymbal strikes are excellent with both, but the KR RK is a bit more full sounding.
Phil Collins's "I Don't Care Anymore" opening drums sound incredible with both tubes, and I personally like the Takatsuki on this track. The strikes are sharper and have more of a wide presence. The KR RK are more emphasized. BTW, the Hellyeah cover of this song is a trip.
Dave Matthews Band "Ants Marching (Live at State Theater, Sidney, New South Wales, Australia - March 2005)" is an excellent demonstration of how to show off a tight-sounding tube and amp. The entire track is well-recorded and sounds phenomenal. The snare drum at the opening rings true on both tubes. The bass has more definition with the KR RK.
Jamey Johnson "In Color" shows off male vocals well. There's a lot of thickness to his voice, and I think the KR RK does a better job of reproducing the gravitas. The guitar is cleaner and sharper with the Takatsuki.
Boston "More Than A Feeling" sounds better on the Takatsuki. Personally, one of my top-5 favorite songs of all time. The opening double-tracked guitar and the bass drop-in just sound better. They ring more true on the Takatsuki. On the KR RK everything is just a bit too heavy.
Anne Hathaway's rendition of "I Dreamed A Dream" from Les Mise'rables shows off a (surprisingly) strong female vocal performance. When she ramps up "sha-a-a-A-AAA-AAAAAME!" you can hear how well a tube can produce power on demand. Both tubes do a fantastic job with this track.
Verdict: Takatsuki 274B is a bit more technically precise while the KR Audio 5U4G Riccardo Kron Anniversary Edition wins in tube warmth. Dealer's choice - both are excellent tubes, each with their own best traits.
Feel free to ask me to test specific tracks if you wish.