For any GF4TI card brand makes almost no diff what-so-ever. Perf, o/c'ing and features are 99% down to the chipset and type of RAM used. Leadtek and Gainward are considered the absolute best for image quality, for GF3 cards they're great, but it makes very little diff with GF4TI cards.
In any case, 4600 is NOT a wise buying decision. You should only consider a 4200-128MB or 4400. 4200-128MB usually reach 4400 speed (easily within 10% of a 4600), enhanced 4200-128MB cards (Suma Special Edition or Asus Deluxe) are clocked at 4400 speeds and reach 4600 speeds (or higher). 4400 are within 10% of 4600 and unlike the 4600 they o/c pretty well too. With Rad9700 seemingly blowing the 4600 away, and the new nVidia cards due out over the next few months it makes no sense to buy a 4600.