Sounds to me like you could benefit from the extra two cores the phenom II has to offer. I would get the 1055t and overclock it. Just remember though that the i5 overclocked will be more powerful per core so make your decision after you decide how much you can really use those two extra cores.
Just a random array of benchmarks:http://www.anandtech.com/bench/Product/191?vs=147
I compared those two so you could see them at the same clockspeed. I've read about the 1055t being overclocked to 4-4.2GHz and the core i5 to 4+ to 4.3 or something. So this is a more accurate comparison of the two if you will overclock.
So if you can use the cores depends on
a. what programs you use
b. how much you run at the same time (giggity)
Hope that helped.