At the time I had my personal justifications for picking my P90 over the P345.
I was interested in a large frame durable .45ACP pistol. I already owned several Rugers, so I already had faith in the Ruger brand. In addition I did not like the magazine disconnect on the P345. Yes it can be disabled, but still I didn't want to modify the pistol. I also liked the slightly longer barrel on the P90.
The P90 has been a pleasant surprise on accuracy. It seems on some pistols I work a little to make sure I am holding correctly to hit the target, but with my P90 it just seems I point and hit without any effort.
Having said that, I am now looking to add a P345 to my collection when possible.....ok, when the wife let's me spend the money.