Apex 1.4.1 was what I was running before flashing the new 3 part GB. I absolutely loved the Apex rom, but was ready to try something new....so here I am with GB
The battery life isn't as good as with Apex, but it hasn't prevented me from using the phone like I normally do. I have been able to get things in good shape using SetCPU. I have started to get used to using the standard launcher too, I was using ADW-EX on Apex.
The standard launcher is sweet! I love the new app drawer button location and settings (group apps), and I'm digging the dock bar setup. The blur is very much improved, and does run smooth. The new keyboard is very nice, and has a cursor that is easy to place to correct or add words. The only blur widget I use is the new social networking which is AWESOME! The dialer and contacts works very well on GB, and I haven't had any issues with any of my apps not working.
I did have a few "OMG, what have I done!" moments during the install and the dreaded red "M" bootloop issue. So learn how to SBF, if you don't know, before you try this. I would just recommend doing a nandroid of the Apex, SBF and install the 3 part GB if you decide to try it. Make sure you use the D2 bootstrap as well.
Overall I am very pleased with GB, only thought about going back to Apex once or twice....but I'm past that now