It's like this as far as I know.
Ti 4800 = Ti 4600 8x
Ti 4800 SE = Ti 4400 8x
Ti 4200-8x = Ti 4200 8x
Ti4600/Ti4800 -> 300/650
Ti4200 128MB 4x -> 250/444
Ti4200 64MB 4x / Ti4200 128MB 8x -> 250/513
The Ti4800 is nothing more than a Ti4600 with AGP 8x instead of 4x. That's all.