I'm not aware of any dual core sempron's, those are all singles.
It's very comparable to an Athlon II 240 X2, clock for clock. But the E3300 is a better overclocker. A 240 would struggle to hit 4ghz, and E3300 would hit 4.2-4.4 with good air cooling no problem.
I had an E3200, and it scored the same in benchmarks as my Athlon II 245 when clocked the same. However, the E3200 I got to 4.2 ghz, the 245 only made it to 3.9ghz. So I would pick an E3300 celeron over the comparable AMD cpu anyday.
''yet unknown E3000 revision''
Whats that suppose to mean? They are based on wolfdale core architecture, same as the E8000 series.