I did a direct comparison between my 9" SME V and my 12" SME V-12 arms on my SME 30/12 turntable in June. The armboard can be rotated 180 degrees to facility the comparison. Tonearm cable and cartridge were the same. Both arm/cartridge combinations were aligned using two custom MINT protractors specifically designed for the Air Tight PC-1 Supreme and the two SME arms.
After about 5 LP sides listening to various types of music, it was quite clear to me. The V-12 arm in my system sounds better. Basically, I hear more music and it sounds more natural. I presume this is due to the lower tracking distortion from the longer arm, but I'm not really sure. The analogy I can use to help describe the difference is this: It was like going from a two-way, two driver compact speaker to a three-way, three or four driver floor standing speaker. The sound is bigger and the frequency range is more extended WITHOUT any loss of coherence. Micro dynamics and detail are also better. It is easier to get absorbed in the music and I am less conscious that I'm listening to equipment reproducing the music.
Another interesting advantage that the SME V-12 arm has over the SME V is that it is designed to be balanced with the extra counterweights as close to the pivot/bearing point as possible with a cartridge weighing around 11 grams. My Air Tight Supreme is 11.5 g so the counterweight is much closer to the pivot/bearing than it is on my SME V. This lowers the inertia of the arm and it could account for some of the improved sonics. The magnesium armtube is so light, that the added length does not add much weight to the overall assembly.
I have not heard other 12" arms in my system, but based on this comparison, I recommend the new SME V-12. I have not heard the similar 12" SME 312S arm.
