Okay, I'd like to get some swim jig heads for my 4.8" Keitech Fat Impacts and my 3.75" Rage Swimmers. I'm leaning towards the Dirty Jigs Matt Allen swim head but wondered which size would be best for each of these baits?

There's LOTS of options these days for swimbait heads. I usually carry 3 types.

 

When I'm fishing really rocky areas that I know I'm going to break off several times, I use the cheap Cabela's brand "mean eye" jig heads for swimbaits. They are inexpensive, sharp, and have nice plastic keepers. I use these when I'm fishing rivers mostly. 

 

When I'm not so worried about donating swimbaits to cover, I really like the Keitech tungsten brand ball head jigs. They come in tons of hook sizes and weights, and also double as great jig-worm heads. These keitech heads are great for smaller finesse swimbaits. 

 

Last year I started using the new Outkast Tackle Goldenye swim jig heads that Josh Doulgas developed, and they are pretty darn amazing. I'm going to alternate between these and the keitechs. 

 

Size wise, it depends on how deep you'll be fishing these. I find that 1/4oz is a good all-around size for 8 feet or deeper. It's good to have several weights & hook sizes to switch things up on the fly. 3/8ths seems to be very popular for deep water fishing (ledges and whatnot) and to use in current. I'd load up on 3/16th, 1/4oz, and 3/8th which should cover you in shallow/mid/deep depths. 

I started using 6th Sense this year and so far I really like them. 

http://www.santonelures.com/store/store_product_detail.cfm?Product_ID=11&Category_ID=3

"...When I'm not so worried about donating swimbaits to cover, I really like the Keitech tungsten brand ball head jigs... "

 

I toss the Keitech tungsten jigs with single mono weed guard.

 

Have you found a way to consistently get a Keitech bait to stay on? I use super glue, but it is 50/50.