I used to play a very similar live setup using Amplitube 2. The only difference was the effects chain in Logic 8 and the interface. I thought I was getting good tone but did feel like it was lacking.
I have recently dumped my software "rig" and went with a POD X3 Live. The tone is 300% more realistic, there is absolutely no perceivable latency and it is easier to setup and configure. I will never play through software again... unless it is POD Farm!
15" MBP 2Ghz Core 2 Duo 6GB RAM, 2 320GB LaCie Quadra Drives, MOTU 828mk3, Logic 9 on SL 10.6
"There is no such thing as an old song, just bad ones."