The topic that's generated the most confusion seems to be the importance of the CHA stat.
I'm going to start off here by saying that it is, as a general principle, impossible to prove a negative. I can't prove to you that CHA has no effect on charm duration. The way statistics works is to start with a null hypothesis (that there is no difference between two conditions) and test whether the evidence shows that you can reject that hypothesis with a specified level of confidence. I.e. you are testing whether or not you can prove a positive effect.
TLDR, the result is:
Unable to reject the null hypothesis that CHA has no effect at the 95% level.
To test this I grabbed a Greater Spurbone in Emerald Jungle and parked it on the south wall. I was level 50, the mob was blue-con, resisted Beguile twice and hit for an observed max of 100, so probably level 38-39. I took off all gear with any CHA on it to take my CHA stat down to its base of 115 (because I followed the folklore and made my character according to the guide …) and proceeded to recharm on each break for around 2 hours. I then put on all the CHA gear I could find, applied the CHA buff to take my CHA up to 226 and repeated the process for another 2 hours or so. This resulted in around 1200 individual tick trials for each condition, and the results are given below:
Input data 1:
File: L50 EJ Gt Spurbone CHA 115.txt
Total trials: 1157
p charm success (per tick): 0.9742
Wilson Score lower bound: 0.9647
Wilson Score upper bound: 0.9836
Input data 2:
File: L50 EJ Gt Spurbone CHA 226.txt
Total trials: 1294
p charm success (per tick): 0.9847
Wilson Score lower bound: 0.9776
Wilson Score upper bound: 0.9915
probability difference: 0.0104
Newcombe-Wilson difference interval: -0.0117, 0.0117
Not significant at 95% level
To illustrate this further, here's a diagram showing the extent to which the two Wilson Scores overlap:
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Now I know that some will be tempted to carp that the increased CHA did show a minor increase in the central success probability number. Unfortunately this fails to appreciate the actual nature of the Wilson Score. The actual probability for each condition may lie at any point within the upper and lower bounds, and these overlap substantially. Furthermore, 95% confidence (2 sigma) is pretty weak-sauce as far as confidence goes and represents the lowest level at which we can start talking about any real difference.
One factor that might come into play is an adjustment called continuity correction. This is employed to ensure that probabilities stay within the 0-1 bounds and becomes more important as the probabilities approach closer to 0 or 1 (as seen here). The programs use continuity correction in their default state, but this does lead to slightly wider Wilson Score intervals. I turned continuity correction off (you just need to change a boolean constant in the code), but it still failed to produce a significant result.
My personal feeling is that the results for the 115 CHA condition just happen to be on the lower part of the range - all my preliminary results were closer to 0.98. But it doesn't really matter, the statistics involved are capable of taking that into account, and do so here.
As I said above, I encourage you to test this for yourselves. Getting the data is rather boring, but the more data the better.
How does this affect standard guidelines? Newbie enchanters should put their points into STR, so they can carry more fine steel back to town to sell.