Not sure on this but was thinking maybe Istomin?
Well he is top 50 material and he is just about to surpass his previous best ranking of like 39. Could be top 30, but honestly, for someone listed only 6'2" his footwork is kind of poor.. I mean he hulks around like he is Isner's height sometimes yet Del Potro moves 1000 x better than him. However, he does have a very clean all-around game regardless.