I wouldn't get too tied up with buying a specific card or brand. Chipset and RAM type dictates almost all perf and potential. Even at default clocks all 4200 beat the GF3TI200 and full ATI Radeon8500. Even so the 4200-128MB cards are a much wiser buy. What you want to look out for is the type of RAM used on the 4200 cards.
4200 core's o/c to 280-320.
4.0ns RAM is standard on all 4200 cards and averagely o/c to 550 (128MB def 444, 64MB def 500).
3.6ns is more common on 64MB cards but can easily be found on 128MB cards and o/c to around 620!
4400 def is 275/550 with o/c around 300/620.
4600 def is 300/650 with o/c around 320/720.
You can read the ns rating off the RAM chips, 2nd line down last 2 numbers. Fancy HSF designs do very little while RAM HS do nothing to enhance o/c. The 4200 is defiitely the best buy for a budget conscious person, while the 4600 is the best buy for those with the cash. On a tighter budget the GF3TI200 and Rad8500/8500LE still offer great perf, esp for slower (< 1ghz) CPUs.