Having just finished watching FMA:BH I can say Brandley is a beast when it comes to melee fighting. Even with their speed equalized, they reflexes were already quite evenly matched. What its really going to come down is a battle of skill, strength and stamina.
However there is one big detail that I feel gives Geralt a major edge against Bradley, which is being able to use Signs. Simple as they are, they give Geralt many means of attack and defense against Brandley. Quen can absorb blow, Yrden slow Brandley greatly, Aard throw him off balance and Igni to force him back. Unless Bradley knows before hand about Geralt's Signs, he's at a major disadvantage. Yet he'd no doubt try to disable or limit Geralt's capability to use them, such as a percision cut to the hand or even making him lose a finger.
But to make things simple let's go with a pure sword fight. In this case I feel its a very even match. Geralt does have more experience, being a good 30 to 40 years older, being a very adapt fighter against human, monsterous and supernatural foes. Brandley will push the WItcher's skills and reflexes to the max, with no doubt both taking injuries along the way. However Bradley has limits when it comes to his stamina and injuries he can handle, since his body while in peek condition is pushing 60. Geralt meanwhile doesn't suffer from any age hinderances. Brandley does have the advantage of his Ultimate Eye, yet even it has it's limits. If his sight is obscure it power is voided, along with the fact that unless he can react in time to an incoming attack, foresight means nothing. Plus if Geralt is perceptive enough, he will no doubt try to injury Bradley to limit his sight, considering his Ultimate Eye is an obvious target.
Overall I feel Geralt will win this fight. It will be by far his hardest duel yet he can endure it and match up to Bradley's skill.