What line do you use with 5inch or bigger swumbaits. Im thinking of switching to 20lb

40 lb braid, green, no leader.
Moving baits, I don't think the fish are paying any attention to the line. If you do haul back and try to sling a bigger swim bait, lighter line backlashes = lost lures. JMHO

Is this a new bait?

25lb mono on my big swimbaits. Braid will wind knot and break. For baits up to 6" 20lb will work

new baits, going to start throwing them. Some of them can get alittle pricey!!!!

I fish 40# braid to a 4# section of 25# fluoro. Alberto knot connection for fluoro to braid. I use braid to fluoro because I grew up on gin-clear western lakes where you had 25' of visibility. Just a habit, I guess. I also fish my swimbaits super sloooooow sometimes depending on if I have a neutral bouyancy swimbait or a top hook (Butch Brown Rig) Huddleston 68 literally almost crawling on the bottom.

Since you are talking about swimbait set ups. If you're gonna dedicate yourself to being a diehard swimbait or wakebait fisherman, make sure you get yourself a reel with plenty of guts to handle it. One of the best all-around is the Curado 300.

We have a winner!

20lb P-line CXX, cheap and tough as whale rope. Braid is a no-go unless you're throwing topwater wake baits or have a lot of experience throwing big baits, too much to worry about as far as breaking off on your casts. Mono or Fluoro will be more forgiving on a backlash, which will happen throwing big baits. 25lb+ if you'e going into the 5oz+. base it off of the weight of the baits, not the length, hardbaits and soft plastic weigh a lot different and have more of impact on the line size you use.