A lot depends on the setup what performance you can get out of A1200. The more you overclock the chances are its going to be unstable.
Stability is key to enjoying any computer,and this is what I worked on for some time now and can enjoy web browsing on a very high speed A1200 with no stability issues whatsoever in a standard A1200 desktop.
The bus speed is a important factor here,but a increase in bus speed normally makes the computer unstable, fix this and you have a very fast stable computer.
Here I have 75Mhz bus as standard,but expect for sure a new world record for dram bandwidth on classic amiga, but also expect blizzard card to close the gap to 100Mhz users of apollo card from its current 96Mhz when overclocking is allowed in second half of 2013.