I know of some very accomplished Salmon anglers using 50lb braid on their bottom mount rods, they swear by it.
20lb braid will be thinner than cotton whereas if you fish with 12 or 20lb mono at present, you can afford to up the line strength and still feel a huge advantage. Biggest advantage is that mono floats high in the water column, braid sinks, mono stretches and negates those soft touches, braid is unforgiving, the price of a one shot spool of quality mono is about the same as the various offerings in braid available at present.
Personally, I would be using 12lb braid for spinning for trout, but would up the anti on Salmon and Surfcasting.
Due to braid sinking, expect a greater occurrence of chafing in bottom grinding from the sea bed reducing the line strength (eventually) and reducing the life span of the braid, hence the use of a heavier test braid.
Remember more importantly, if you remove the flex of the mono with braid replacement, you will need a very understanding rod, that can cope with those bigger fights and the style of retrieve is totally different with no margin for error.
The term rip some lips comes to mind also, you will hurt more fish and I have been informed from within the trade, there have already been discussions about banning the use of braid for freshwater due to heightened incidence of fish harm.
A few points to ponder.