Have you ever play against a top 20 world player

Even worse!

I played Magnus here on this site at 960 blitz - thank you Lichess!

Beyond that I played some future ~2700 players when they were tiddlers - McShane, Howell, (I think) Vallejo and maybe some others that I don't remember as they didn't have 'future super GM' on their foreheads (although for McShane it was obvious even then....)

I sat with with McShane on the train after the simul, he's a very friendly guy. I was with a friend and McShane caught the same train and came and sat with us. We gave him 5 minutes to get comfy and then bombarded him with chess questions the whole way home! He was happy to talk. He got something out of it though as I told him about a London tournament that was on and he entered it and won. 5K I think. I was at the same tournament and he recognised me and we spoke for a while. He didn't share any of his winnings though...

I played some 20 years ago in an IRL simul against former world #3. It ended in a draw. That was the peak of my chess career. :-)

Yes, he [Luke McShane] always seemed down to earth and not at all arrogant despite his huge talent, also as a child. I remember two games - when I was ~14 and around 190 ECF and he ~11 and around 200, a draw in a French exchange, and then later when I was ~21/22 and he ~18/19 and around 2600, where I got crushed in a Sveshnikov Sicilian as soon as we came out of theory.

His Spectator chess column is also a huge improvement on the rubbish that Ray Keene produced previously...

Matthew Sadler reached 14th ranking some years ago. I played him in a casual game some years before that when he was about 8 years old. Draw!

@piscatorox : Lay off the Keenester, he kept it real.
In all seriousness, he wrote the first chess book I ever owned.

I once played a former World Championship Candidate in an over the board open tournament, which he won. During the game I thought I saw a winning combination, so I played it, then he unexpectedly sacrificed his queen and beat me with a counterattack.