STSF just checks your int/wis against your opponent's int/wis with intelligence being the major factor. Succeeding on the intelligence checks means you get echoes that indicate stackable passive benefits in combat for the duration of your/your opponent's login. It has nothing to do with age but if you are expecting to fight flurrying Cloud Giant/Dwarf nexans, your mileage from it may be limited, conversely if you can maladict hard enough with daggers it will be invaluable against shapeshifters for whom categorically most forms are average to crap intelligence/wisdom. STSF can also offset things like mongoose/hummingbird evasion given enough time to observe the opponent. Hit and run can help in this regard.
Duergar and arials benefit from dex legacies almost equally and are superior in strength legacies, while arial are superior in intelligence legacies.
Don't take speed flurry unless you are comboing the edge with something like Fluid Deceptions for a one round disarm, speed flurry at the moment is more of a flaw that costs edge points and makes flurry parryable than it is a buff to dex sword specs.
Arials will perfect their skills faster and thus have more incentive to level faster but duergar have the raw HP and stats to PK in the midranks, especially as a villager. However everything is a pain in the ass to learn so it's hard to say whether you'll win more fights spamming stab or bash;bash;doublethrust as a duergar at level 25 to 35
