Hmm... it is sounding like 3d10, drop the lowest (rerolling anything below a 6) may be the way to go for a random roll determining stats...
Brian - what did you think of my variation of the point buy method that you suggested?
First of all, I think there might be a small error in the point buy numbers you quoted. There's only a 2 point jump from 17 (11pts) to 18 (13pts), when I think that should be 3 points according to your description. But I used your chart as written for the following. I can correct the numbers as needed, but it will mostly just bump up the point counts of the more powerful characters below...
So I just experimented with both the rolling method you suggest, plus the point buy values. I wrote a dice roller that implements those rolls (3d10, top 2, stat >=6 ) and ran 100 random "characters" through it. Here are the highest, middle, and lowest lineups for that:
#1) 20 19 18 18 18 11 11 11 (avg: 15.8, and worth 77 points using proposed point buy values)
#50) 20 17 15 14 13 10 10 9 (avg: 13.5, and worth 41 points using proposed point buy values), the typical character
#100)15 15 14 11 10 9 7 6 (avg: 10.9, and worth 7 points using proposed point buy values)
Even that lowest character, the 1% worst case scenario, is still a very playable one with a couple of 15s, and the top one is a monster with 5 stats of 18 or higher, which makes think that we may still be a little "high" in the overall scale.
Two ways to trim it down a bit:
If we do the 4 stats with 3d10 (drop lowest) and 4 stats 3d10 (drop middle, which is effectively a 2d10) we get:
#1) 19 18 18 17 16 13 10 10 (avg: 15.2, and worth 64 points using proposed point buy values)
#50) 20 13 13 13 12 10 9 9 (avg: 12.4, and worth 28 points using proposed point buy values), the typical character
#100) 16 13 12 12 9 9 6 6 (avg: 10.4, and worth 5 points using proposed point buy values)
or perhaps a simpler/more elegant method of 2d10 but rerolling any 1s or 2s (which also ensures a minimum stat of 6):
#1) 19 18 18 18 16 15 10 9 (avg: 15.4, and worth 67 points using proposed point buy values)
#50) 17 15 14 14 13 13 12 9 (avg: 13.4, and worth 31 points using proposed point buy values), the typical character
#100) 16 14 12 10 8 7 7 6 (avg: 10, and worth 2 points using proposed point buy values)
For comparison, the traditional D&D method of 4d6, drop low, gives you:
#1) 18 17 16 15 15 14 14 13 (avg: 15.3, and worth 53 points, although the max stat is 18)
#50) 17 15 13 13 13 11 8 8 (avg: 12.3, and worth 22 points)
#100)12 11 11 10 8 7 7 7 (avg: 9.125, and worth -7 points)
So I will leave these numbers up for everyone's consideration. I personally have never been the kind of player to desire super-high stats, because any good DM will simply throw super-hard baddies at you. I like a mix of a few good stats, maybe one exceptional one, and a few flaws. Forces you to have to defer to other players when something challenges your weaknesses.
I think I myself lean toward the "2d10, reroll 1s/2s" as they keeps the namesake 2d10 mechanic, and everyone is ensured of having 2 d10s, but not always 3...
(disclaimer/footnote: The above numbers are just sample sets run 100 at a time. They do not necessarily reflect average probability. But if you want those, I can compute those too