I agree the Bang water skills are still more accurate and stronger than Garou's one, and Bang still doesn't show everything in the manga, with abandonment he will peak. But I think Garou will win this : Garou is impossible to put down except with an overwhelming strength right off the bat : Tatsumaki giving it all immediately will erase him currently but if you let Garou fight and tank and fight again you won't put him down. Garou can tank for hours and hours.
And Garou has now huge stats : with his strength he can clash against Darkshine, he is crazy fast, and has water and wind skills.
Even with abandonment Bang won't be really far ahead from him. So Garou will manage to clash with all out Bang and while on the loosing end in the begining, bit by bit will overpower him and beat him.
(Ivy avy nice choice ^^)