How Usopp fights? By confusing, impairing and incapacitating his opponent.
General Purpose: Smoke screens can allow Usopp to move unseen. Who needs high speed when the opponent cannot see (and predict) you?
Soru: Caltrop Hell, String Dial (if it works), other string-based attacks, slippery ground, some glue-based star… a lot of things could be used against Soru. Usopp would not be able to follow the speed, maybe, but he could make traps around him, making it hard for the enemy to move around, or making him trip at high speeds.
Tekkai: Somehow I think Usopp will make the enemy assume Tekkai in order to resist a series of blows, just so that he can hit Tabasco Star in his eyes while he is immobile and invulnerable. Also, there's Impact. And he could always throw a rotten egg at his opponent's face just to infuriate him.
Geppou: Like Buccaneer said, it is not a offensive move. Very useful to escape Usopp's traps, but you can't use it together with Soru (you need to kick the ground to use Soru), so the speed of the CP9 is impaired. And it makes you a moving target to Usopp's strength: ranged attacks.
Rankyaku: Hide, confuse, counter-attack. And I bet Axe Dial will counter it, or even be used to duplicate a Rankyaku. This is probably the most dangerous move (aside from Shigan) for Usopp, but since it is a ranged move, Usopp will probably dodge and counter it with his own ranged attacks.
Shigan: Now here's the danger. Obviously the Impact Dial can nullify the Shigan, but can Usopp block effectivelly all the attacks of his opponent. Shigan, however, requires close range combat, and I think Usopp will only allow his opponent to come close when he has no other choice.
And all that is not taking in account any new Usopp weapons or dial-enhanced attacks. Hell, it is Usopp: I would not be surprised if he has a ton of new dial-enhanced weapons in his pockets. Almost all of our ideas come from naked, non-enhanced dials and old Usopp tricks. He sure has all four aces in his sleeves in this fight.