I am by no means an expert but I have asked this question alot. I recently just bought a pair of Precision 67/66 journal bearing. My decision was bases on the price , durability of journal bearing vs ball bearing and opinions of people who sell them and people work in the turbo industry but are not biased to one brand. Some people say ball bearings help alot some say you are just throwing money away. My turbos are on the small side and spool quickly in journal bearing, now that may be a different story on large frame turbos. My tuner who I have alot of trust in says that in a drag application ball bearings are a waste for the little gain they provide vs cost. I am on a budget so the journals were right for me. My previous set of turbos were journal and never had any problems. The opinions I got on which one spooled better was focused more on getting the right turbo size, wheel, a/r housing and hot side rather than a journal vs ball bearing. Thats my 2 cents. Hope it helps.
When comparing apples to apples, a well engineered ball bearing will get you into boost a little quicker, but once you are in boost there are very little to no power gains. They do offer improved thrust capacity over a normal thrust bearing system.
The added thrust capacity of the BB setup is it's main benefit IMO. If you're not killing thrust bearings regularly it may not be worth the cost. Keeping the back pressure to boost pressure ratio in control and using a high zinc oil go a long way to keeping the thrust bearing in the turbo even if you like to get as closed to maxed out on the compressor as possible.