I had some free time and cheap media handy, so conducted some tests with my LTR-32123S using XS0X, XS0Z, and XSU1 firmwares. Tests were with 40x Jensen (Princo) and a 735MB VCD image (Mode 2) burned with Nero 126.96.36.199 and tested with K-Probe 1.1.4. No C2 errors were reported on any of the discs.
XSU1 @ 40x (P-CAV)
Burn time: 2:57
C1 Errors: Ridiculously high. Average of 250.
XS0Z @ 32x (P-CAV)
Burn time: 3:06
C1 Errors: Max - 228, Total - 55015, Avg. - 16.301
Comments: Only 9 seconds slower than XSU1 @ 40x, and tolerable C1 error rate.
XS0X @ 32x (Z-CLV: can see 4 zones on disc)
Burn time: 3:32
C1 Errors: Max - 30, Total - 9340, Avg. - 2.758
Comments: 83% lower C1 error rate than XS0Z. Burn time was more affected by P-CAV - > Z-CLV @ the same 32x speed than 40x -> 32x.
Teac combo laptop drive @ max speed 24x (Z-CLV: can see 3 zones on disc)
Burn time: 5:33
C1 Errors: Max - 14, Total - 2258, Avg. - 0.651
Comments: Threw this in to see how the LiteOn 32123s compared to my other burner. 96% lower C1 error rate than XS0Z, 76% lower C1 error rate than XS0X. Unimpressive burn time.
XS0X @ 24x (Z-CLV: can see 3 zones on disc)
Burn time: 3:47
C1 Errors: Max - 30, Total - 9247, Avg. 2.717
Comments: Error rate no differet from XSOX @ 32x. Wanted to see whether the Teac's better C1 Error #s were due to the lower 24x burn speed. The burn time @24x with the LiteOn was much better than the Teac @24x. So much for speed ratings...
In conclusion, XS0X provides higher quality burns at the expense of ~30 seconds per disc - well worth it in my opinion.
P.S. I also tested out some Imation 48x media (CMC Magnetics), and the results (relative to each other) were the same, with the XS0X firmware producing the lowest C1 errors by a sizeable margin. But the C1 error rates in general were through the roof with these discs, which is why I guess everyone says CMC discs suck.