4.8ghz is near impossible on a Phenom II line, unless you got what they call a golden chip. But most of the phenoms will clock around 3.7 - 4.3ghz in a real world overclocking. To get beyond 4.3ghz you need good cooling, and I mean good!
The OC sweet spot for the 1055t is 3.8 ghz.
The max on the stock cooler would be about ~3.4 ghz.