File 5-X25.txt contains an equation for X_ns^+(25) from David Zureick-Brown.
The equation has degree 120 in one variable, degree 25 in the other variable,
and total degree 145.

A simplified, birationally equivalent, equation of degree 15 is:

F :=
-581969591808*y^15+(8014838670080*x-4404001043200)*y^14+(-41609682693120*x^2+56452653488640*x-13915023495680)*y^13+(92700893099360*x^3-280761316376800*x^2+159493673722400*x-
14933069060000)*y^12+(-30585082688160*x^4+639775715296640*x^3-726001846078400*x^2+139045936705920*x+26926378268000)*y^11+(-248093943252880*x^5-442349219358640*x^4+
1725233565340000*x^3-782185700490080*x^2-147166062015440*x+69443905329424)*y^10+(402779743083440*x^6-938292205645600*x^5-1857641144994800*x^4+2632361348910400*x^3-
306693630327600*x^2-254852032601120*x+13392314412400)*y^9+(12633473060790*x^7+2110578905302210*x^6-923393467799170*x^5-4115249446089350*x^4+3353623139306050*x^3-
1032428914569370*x^2+537837263115530*x-169133487032610)*y^8+(-510769293719472*x^8-764040187578736*x^7+4449123068735264*x^6+189865321403568*x^5-5886911008577440*x^4+
5376086422648048*x^3-3546631090030176*x^2+1610275711626704*x-289173886626672)*y^7+(274991292376935*x^9-1603456881312631*x^8-2516812181932308*x^7+6316257323269252*x^6-
957012558017406*x^5-5153489537210290*x^4+6667398230664284*x^3-4457289058559628*x^2+1497050283955407*x-181939559110351)*y^6+(212674155341045*x^10+1326926378829690*x^9-
2403647282993787*x^8-3335158200442616*x^7+8717011733678714*x^6-6169534955978132*x^5-173328492267070*x^4+2928528525017128*x^3-1815509671851471*x^2+418665880985834*x-
22259861458151)*y^5+(-158137421481500*x^11+387808056110260*x^10+2021184370686120*x^9-3662924484240400*x^8-1460097708668520*x^7+9185916404016600*x^6-10104188978326240*x^5+
5958004465794320*x^4-2560078228508700*x^3+932938626728980*x^2-244169150593320*x+29472598677600)*y^4+(-45338867474325*x^12-514304692627350*x^11+477930836924420*x^10+
1847953680657270*x^9-4673744371509265*x^8+2464431634315620*x^7+3632240121801760*x^6-7116554032904340*x^5+6065409844504345*x^4-3196848740759790*x^3+1058702289468700*x^2-
197779206720450*x+15146569867085)*y^3+(23741611524375*x^13-41404384246625*x^12-528078389255850*x^11+725455683803350*x^10+898816900963945*x^9-3506447340959183*x^8+
4179429687170676*x^7-1735686984917964*x^6-989272772046983*x^5+1596703295159185*x^4-874188336701738*x^3+251753257474966*x^2-37567727519129*x+2124153726207)*y^2+
(6165902322000*x^14+38440955487500*x^13-39779084171800*x^12-248312553020800*x^11+602342404021800*x^10-257325106242740*x^9-797153627288464*x^8+1567176577183328*x^7
-1400639287976672*x^6+730001535512676*x^5-223304553751480*x^4+33618765517856*x^3+185503791848*x^2-750534448572*x+58351497696)*y+4*(x-1)*(5*x^2+3)*(102765038700*x^11+
549462577475*x^10-836794437650*x^9-3310667070165*x^8+8044178520976*x^7-7432607804666*x^6+3619319107492*x^5-978497444562*x^4+140603632948*x^3-10182002281*x^2+743399742*x-44855865) ;

Though already much smaller, it is likely that a smaller equation exists.