Are you asking for a ROM or a RADIO?
Actually, either way, it doesn't matter. You'll have to find the best combination for yourself. Different phones react differently to radios. Same with ROM's.
So yeah, trial and error, rinse and repeat.
No. All Radios you see on the RADIO thread are fully compatible for each and every DZ/G2. So flash away, test radio for 4-5 days minimum and see what works for you.
Like I said, it's different for everyone.