I'm the OP of this thread, and ironically, my turntable is a Technics SL1210 M5G.
12-22-14: Johnjohn
I agree with the original post that you need a quality turntable and arm to really hear this cartridge. I use mine on a Linn/Ittok with good results- lots of ambiance and leading edge detail. I put it on a Technics 1200 and didn't hear any improvement over a 440MLa.
However, I agree that out of the box, the standard SL1200 sounds murky, but that's not due to the tonearm or direct drive; it's a lack of damping and it's easily and cheaply fixed. The M5G starts with upgraded tonearm wire, and I added several tweaks--better headshell, tonearm wrap, KAB's tonearm fluid damper, Oracle Groove Isolator sorbothane mat, and a stack of gel pads, butcher block, Vibrapods, and brass cones for the platform. Every addition improved the clarity, linearity, and dynamics. From there I got improvements as I upgraded the phono stage. Throughout all these upgrades the AT150MLX shone through with more clarity, detail, transparency, bandwidth, dynamics, and musicality.
I haven't heard the AT440MLa, but from the beginning and ever since, my AT150MLX has always outperformed my Denon DL-160. Similar tonal balance, but the AT consistently digs down deep and comes out with more music.