So, I just drove SpeedDemon's 2004 330i Sportpack Manual

A huge thanks to him for lending me his time, and his car
At face value, the difference is quite substantial. It's not out of this world, but the with the bigger engine, and the manual gearbox, it was quite a bit more impressive. I could definitely feel the extra torque, and it really shunts in the first two gears. There's also a little extra excitement when you pass 4500rpm which i noticed

The car sounds better, and quite a bit more fun than the 325i i drove.
It is however, still very refined, which takes away from some of the excitement, but then again, you have to consider it for what it is. And for what it is, its pretty damn cool. With two passengers it'll happily accelerate relentlessly. SpeedDemon's car apparently has a decat and a Van de Graaf back box, and I was very impressed with this exhaust - as it was not too loud, nor was it intrusive at anytime. It made noise when you wanted it to, but could quiten down on teh highway and be very civil. I do think, however, that the car simply doesn't make enough induction noise for my liking, but that can be fixed easily
Overall, it's definitely a huge improvement over the 325i auto that i drove. It's no M3, but still a fantastic car to drive, which has a bit of personality if need be.
Once again, a huge thanks to SpeedDemon for giving me the opportunity to experience the car.