Your winning solution (aeilprst: 552) really only gets 344.

Indeed. I had de-dup code that didn't.

Once properly de-duped, I get aeilprst: 344:

ail ails air airs aisle ale alert alerts ales alit alp alps alter alte
+rs ape apes apse apt apter are ares arise art arts as asp 
aspire aster astir at ate ear earl earls ears east eat eats era eras e
+rst esprit eta etas ilea irate ire ires is isle islet it
its la lair lairs lap laps lapse las laser last late later lea leap le
+aps leapt leas least lei leis lept lepta lest let lets liar 
liars lie lies lip lips lira liras lire lisp lisper list lit lite lite
+r liters litre litres pa pail pails pair pairs pal pale paler
pales palest pals par pare pares pars parse part parties parts pas pas
+t paste pastel pastier pat pate pates pats pea peal peals pear
pearl pearls pears peas peat peats pelt pelts per peril perils pert pe
+st pet petal petals pets pi piaster piastre pie pier piers pies
pilaster pile piles pirate pirates pis pit pita pitas pits plait plait
+s plaster plat plate plates platies plats plea pleas pleat pleats 
pliers plies praise prate prates pries priest prise psi rail rails rai
+se rap rape rapes rapist raps rapt rasp rat rate rates rats re 
real realist reap reaps relit rep repast reps res rest retail retails 
+rial rials rile riles rip ripe ripest rips rise rite rites sail 
sale salt salter saltier sap sari sat sate satire sea seal sear seat s
+epal sepia septa sera serial set silt sip sir sire sit sitar site 
slap slat slate slept slier slip slit spa spar spare spat spate spear 
+spelt spiel spilt spiral spire spirea spit spite splat split sprat 
sprite stair stale staler staple stapler star stare steal step stile s
+tir strap strep stria striae strip stripe tail tails tale tales 
tali tap tape taper tapers tapes tapir tapirs taps tar tare tares tarp
+ tarps tars tarsi tea teal teals tear tears teas ti tie tier tiers 
ties tile tiler tilers tiles tip tips tire tires tis trail trails trai
+pse trap traps trial trials tries trip tripe tripes triple triples 
trips tsar
[download]

But now that is in second place to aeinprst: 346

air airs an ani anise ant ante antes anti antis ants antsier ape apes 
+apse apt apter are ares arise arisen art arts as asp aspen 
aspire aster astern astir at ate ear earn earns ears east eat eats en 
+ens entrap entraps era eras erst esprit eta etas in inapt inept 
inert ins insert inset instep inter inters irate ire ires is it its na
+e nap nape napes naps nastier neap neaps near nears neat nest 
net nets nip nips nit nite niter niters nites nitre nitres nits pa pai
+n pains paint painter painters paints pair pairs pan pane panes 
panier paniers pans pant pantie panties pantries pants par pare parent
+ parents pares pars parse part parties parts pas past paste 
pastern pastier pat pate pates pats pea pear pears peas peat peats pen
+ penis pens pent per pert pertain pertains pest pet pets pi 
piaster piastre pie pier piers pies pin pine pines pins pint pints pir
+ate pirates pis pit pita pitas pits praise prate prates pries 
priest print prints prise psi rain rains raise ran rani ranis rant ran
+ts rap rape rapes rapine rapines rapist raps rapt rasp rat rate 
rates rats re reap reaps rein reins rent rents rep repaint repaints re
+past reps res resin rest retain retains retina retinas retsina 
rinse rip ripe ripen ripens ripest rips rise risen rite rites saint sa
+ne saner sap sapient sari sat sate satin satire sea sear seat 
sent sepia septa sera set sin sine sip sir sire siren sit sitar site s
+nap snare snip snipe sniper snit spa span spar spare spat spate 
spear spent spin spine spinet spire spirea spit spite sprain sprat spr
+int sprite stain stair star stare stein step stern sterna stir 
strain strap strep stria striae strip stripe tan tans tap tape taper t
+apers tapes tapir tapirs taps tar tare tares tarn tarns tarp 
tarps tars tarsi tea tear tears teas ten tens tern terns ti tie tier t
+iers ties tin tine tines tins tip tips tire tires tis train 
trains traipse trap traps tries trip tripe tripes trips tsar
[download]