You can get the 965BE and get decent performance if you game a lot. That would give you advantage in video encoding as well.
But the 1055T would definitely give you an extra boost for video encoding. You just have to decide if its worth the extra $30.
Install of the CPU? Well, pretty easy and less finicky with the AM3/AM2 sockets. 5 minutes for someone who has no clue what they are doing but is reasonably intelligent.
Big push? From your x3? yes. if the encoding can use all cores (which it likely can) than there will be more than a 100% improvement. Higher clockspeeds, twice the cores and each core more efficient and a slight amount better than the original phenom core.