The old HKS VS Garrett arguement.
It really is a mixed bag.
Have a look at the -5 vs 2530 results.... There are some cracking results out there with the -5's. Gav from WA, Tangomatt from Vic are brilliant examples of the 'inferior' garretts can do. There are arguements for both sides. Rob from RIPS in NZ only uses the Garretts and look at the numbers he is ripping out of those things!
I think it comes down to not just the huffer hanging off the side of your engine but the package. Headwork, cams, turbo size, exhaust size.... You cant just whack a 'big brand' turbo on and expect X,Y and Z.