Since 2011 I play the white side in either Ruy Lopez or the Berlin variation of Ruy Lopez with Nc3 aka Spanish Four Knights. I have also Scotch Four Knights in my repertour as well. There are a few lines where Scotch Four Knights can transpose to Spanish Four Knights positions that can also be reached via Ruy Lopez and I have reached this in several over the board games.
Spanish Four Knights is a universal system that can be reached via Ruy Lopez Berlin, Three Knights game, Vienna Game, Nimzovich defence, Petroff Defence and Alekhine defence. Four Knights are relatively common in Petroff events at at ICCF, I have both met it several times in various versions and played it myself several times. My statistics vs a local FIDE Master who is an Alekhine expert increased much when I got him out of hes pet defence by playing 2 Nc3.
I played the Berlin variation of Ruy Lopez with Nc3 aka Spanish Four Knights in all of my white games in five Petroff tournaments at ICCF, including in one final tournament.
I have also played it in team matches for Team Sweden as well as in over the board team matches for local club. I have also played it in normal tournaments, both over the board and at ICCF. I played Scotch Four Knights in one event to get more variation and also in some rated events but Scotch Four Knights appers rather boring in Correspondence Chess. I switched into a normal Petroff mainline instead in later events.
My conclusions are that both Spanish Four Knights and Scotch Four Knights are very good openings in over the board games but not strong in Correspondence Chess vs players with a elo over 2100 where black often equalizes. Therefore I switched towards Ruy Lopez, including a main line vs Berlin. I also switched into a mainline vs Petroff and a mainline vs Alekhine.
|2016||WSTT/RD/019 - Russian Defence, C42||4,5/8: +2 =5 -1||3rd place .|
|2017||WSTT/RD/022 - Russian Defence, C42||6/8: +4 =4 -0||1st place .|
|2017||WSTT/RD/023 - Russian Defence, C42||5,5/8: +3 =5 -0||2nd place .|
|2018||WSTT/RD/28 - Russian Defence, C42||4,5/8: +2 =5 -1||3rd place .|
|2018||WSTT/RD/Final 05 - Russian Defence, C42||4/8: +0 =8 -0||I have no games left but the tournament is not completed yey .|
|2019||WSTT/RD/30 - Russian Defence, C42||6/8: +4 =4 -0||2nd place .|
|2019||WSTT/RD/32 - Russian Defence, C42||2,5/4: +1 =3 -0||I have 4 games left in this 8 game tournament .|