I manage for clients and trade on avg 200-300 contracts per position(block allocation trades), sometimes thru one large trade and sometimes broken up into 3-5 trades depending on the time of day and/or volume, econ news events, etc.
ES is very liquid, generally speaking, unless you are in after hours session in which case you need to be a bit careful about liquidity/spreads if you are trading anything over 30-50
During main market session, generally speaking, If you are trading between 1 and 25 contracts you have absolutely nothing to worry about. Your fills are quick.
I also trade euro futures(6E), and pound futures (6b), never had a problem with large size with them either. Although i do have more instances of breaking up my orders on 6e and 6b into multiple ones bcuz they arent quite as liquid as the ES.
Anyone else who trades large size futures wish to chime in on this subject?