Very very true. Latency and particularly the actual liquidity of the underlying will surprise a lot of extremely successful and enthusiastic paper traders when they first jump into live trading. That of course doesn't mean paper trading isn't important or that it is irrelevant. It is a NECESSARY part of a wannabe trader's training for so many reasons. But building a paper account up from $50k to $500k in a month or two (I did that) doesn't mean you will be a consistently successful live trader when you start playing for keeps. (I wasn't.)
I don't know, All I know is that in my experience sim trades give you better fills than real time cash account fills. Might have something to do with bid ask or the fact that you are not actually participating in the market.
BOUGHT 200 shares XLV @ 141.28 Stop at $135 Target (initial ) $155 rationale - broke out of base (not sure if its base or cup , one mans base is another mans cup ) Targeting 155 for partial sell (then will re-examine chart) for 2:1 R/R