Thinking of rooting G2 phone - OS recommendations?

[JT9824]

I've had my T-Mobile/HTC G2 for ages, and it's still on Android 2.3. I'd like to root the phone and install another OS: perhaps Cyanogenmod, or some other Android variant. However, I've been told that this will slow down my data connection, and make calling less reliable. Is there any Android variant with which I can maintian 4G speed and good call reliability? Thanks.