Gladiator fightning at full confidence is faster than Flash, that can always try to steal his speed, slowing down him, considering Gladiator has never met him, he wouldn't try a speedblitz but probably fight at same speed of Flash, who considering can only use the IMP or try a full blast of Speed Force, may success, maybe using a lack of confidence of Gladiator that to Flash would appear only as esitation, but it would be a lucky shot, cause Gladiator has fought guys more powerful than Flash, only a lucky shot can grant Flash the victory here.
This depends on where the fight takes place and whether Gladiator is defending the Shi'ar Empire or just fighting for the hell of it. If he has a cause I'd take Gladiator. Random fight; toss up. Glads might get so confident he overwhelms the influence of the speed force. I mean, Gladiator can do anything he sets his mind to so long as his will doesn't falter. If Gladiator stays focussed, Flash is f*cked.
Gladiator isn't faster than Flash. Based on his powers though, if he put his mind to it and his will didn't waver he could keep up with Flash. Gladiator's physical powers (like a GL) are based on his will and confidence. If he believes he can do something, he can. I'm not sure Glads is under normal circumstances capable of keeping up with Flash, but if he had to in order to protect the Shi'ar Empire he would.
Some of y'all are debating the "Flash" part of it, and completely overlooking the "Flash at ONE with the Speed Force" part of it. If most of y'all don't really understand what that Flash is capable of, I suggest looking up Kingdom Come.
Flash can surpass lightspeed and if he wants perform time travels, you're still refering to the Flash of the 90' comics, when Wally wasn't so expert in using the Speed Force.