I have Srint and recently upgrade my blackberry 8330 from OS 4.5 to OS 5.0 (the leaked version). What I have been observing is that while in a call, my phone would shut down on itself for no reason. Sometimes I am on the call, and getting a text message, it would cause my phone to shut down.
I don't know if anyone who upgraded their 8330 from 4.5 to 5.0 experiencing the similar problems, but you know it takes a long time for this phone to reboot.
You could always use an official release, then strip it down using the instructions in the "How to" section using the Memory Optimization Procedure. I started with the Boost version OS 5 which works flawlessly but is pretty overweight. Then using the techniques from the MOP now have 32Mb of file free memory and my bb purrs. I admit I was tempted to install another OS before I tried this. But there are advantages to starting with an officially released OS. Good luck.
Posted from my CrackBerry at wapforums.crackberry.com