Bass Pro has a sale on some Owner Flashy swimmers now and I wanted to pick up some. I want to get the right size to go with my 3.8 Keitech paddle tail swim baits. Do you think the 3/0 or the 5/0 would be the better size to go with?

I would go with the 3/0.  The 5/0 is used with baits like the Skinny Dippers which are 5” long and the 4.8 keitechs.

As revival said use the 3/0 for the 3.8 inch baits but  I do better with the bigger keitechs on the 5/0 hook.    Give them a try.   

3/0 is good for the 3.8 and 4.2(3?). Get some of the colorado blade too - Bluegill flash keitech with the gold colorado blade is stunningly effective here in texas. 

 

If you can, get the next sized up in CPS springs - they ones they come with are a bit small for the keitechs. It'll work, but you'll go through them faster.