long or short ribbon for 4khz+?

[thadman]

I'm designing a dipole WWTMWW and have to decide what high frequency tweeter I'm going to use for the region 4khz-20khz. All of the drivers will be operating dipole (RS225s are open baffle and the RS52 and ribbon will be front and rear firing).

I have to decide between a short ribbon or long ribbon. I don't want to spend >$500, but less is always better. I am currently considering the Fountek NeoCD2.0 (120mm ribbon), Fountek NeoCD1.0 (1.5" ribbon), and the Aurum Cantus G2si (I can get these for $60/each).

short ribbon
advantages:
-shorter length allows closer CTC spacing for RS225s in WTMW
-much wider vertical dispersion (1.5" vs 5"...pretty significant difference)
-cost 1/2 $

disadvantages:
-poor efficiency and lower maximum output (by ribbon standards), the NeoCD1.0 hovers around 90dB
-poor non-linear distortion

long ribbon
advantages:
-incredible efficiency, the NeoCD2.0 is between 98-100dB over its operating range
-better distortion performance

disadvantages:
-height makes CTC spacing difficult
-extremely poor vertical dispersion
-cost $120-130/each

At this point, I'm leaning towards the NeoCD1.0 if it's dynamically capable. If we assume 90dB efficiency and add 6dB for baffle step and another 6dB for dipole radiation, we achieve 102dB. If we increase power to 16 watts, we're able to achieve a maximum of 114dB. Is this high enough for most dynamic recordings?

Is baffle step already figured into the sensitivity of the tweeters?

Is the vertical dispersion of ribbons (even short ones) already poor enough that they absolutely require on-axis listening? Adjusting the vertical height ribbons so that my ears lie within the 5" length of the NeoCD2.0 seems doable...but wildly impractical with the NeoCD1.0.