letter combinations to make words
Ruby, 116 97 92 characters
9.times{|n|p IO.read('w').split.group_by{|s|s.chars.sort}.max_by{|k,v|k.size!=n+3?0:v.size}}

The wordlist is expected in the file w in the local directory. Program runs less than a second.
Output:
[[&quot;A&quot;, &quot;E&quot;, &quot;T&quot;], [&quot;ATE&quot;, &quot;EAT&quot;, &quot;ETA&quot;, &quot;TAE&quot;, &quot;TEA&quot;]]
[[&quot;A&quot;, &quot;E&quot;, &quot;L&quot;, &quot;S&quot;], [&quot;ALES&quot;, &quot;ELSA&quot;, &quot;LEAS&quot;, &quot;LESA&quot;, &quot;SALE&quot;, &quot;SEAL&quot;]]
[[&quot;A&quot;, &quot;E&quot;, &quot;L&quot;, &quot;S&quot;, &quot;T&quot;], [&quot;LEAST&quot;, &quot;SLATE&quot;, &quot;STAEL&quot;, &quot;STALE&quot;, &quot;STEAL&quot;, &quot;TALES&quot;, &quot;TEALS&quot;, &quot;TESLA&quot;]]
[[&quot;A&quot;, &quot;C&quot;, &quot;E&quot;, &quot;R&quot;, &quot;S&quot;, &quot;T&quot;], [&quot;CARETS&quot;, &quot;CASTER&quot;, &quot;CATERS&quot;, &quot;CRATES&quot;, &quot;REACTS&quot;, &quot;RECAST&quot;, &quot;TRACES&quot;]]
[[&quot;A&quot;, &quot;D&quot;, &quot;E&quot;, &quot;E&quot;, &quot;G&quot;, &quot;N&quot;, &quot;R&quot;], [&quot;ANGERED&quot;, &quot;DERANGE&quot;, &quot;ENRAGED&quot;, &quot;GRANDEE&quot;, &quot;GRENADE&quot;]]
[[&quot;A&quot;, &quot;E&quot;, &quot;G&quot;, &quot;I&quot;, &quot;L&quot;, &quot;N&quot;, &quot;R&quot;, &quot;T&quot;], [&quot;ALERTING&quot;, &quot;ALTERING&quot;, &quot;INTEGRAL&quot;, &quot;RELATING&quot;, &quot;TRIANGLE&quot;]]
[[&quot;A&quot;, &quot;A&quot;, &quot;C&quot;, &quot;E&quot;, &quot;I&quot;, &quot;N&quot;, &quot;R&quot;, &quot;S&quot;, &quot;T&quot;], [&quot;ASCERTAIN&quot;, &quot;CARTESIAN&quot;, &quot;SECTARIAN&quot;]]
[[&quot;A&quot;, &quot;D&quot;, &quot;I&quot;, &quot;I&quot;, &quot;M&quot;, &quot;N&quot;, &quot;N&quot;, &quot;O&quot;, &quot;O&quot;, &quot;T&quot;], [&quot;ADMONITION&quot;, &quot;DOMINATION&quot;]]
[[&quot;A&quot;, &quot;C&quot;, &quot;G&quot;, &quot;H&quot;, &quot;I&quot;, &quot;I&quot;, &quot;L&quot;, &quot;M&quot;, &quot;O&quot;, &quot;R&quot;, &quot;T&quot;], [&quot;ALGORITHMIC&quot;, &quot;LOGARITHMIC&quot;]]