AFAIK, there's two symbols tracking the S&P 500 Cash price: SPX.XO (from CBOE) and SP500.X (from CME Indexes). Both of these refresh every second. Is there any other S&P 500 Cash symbol which refreshes more frequently?

The SP500.X symbol has a Bid and an Ask price, so I kind of expected anything that was tradeable would be refreshed on a tick by tick basis, rather than every second?

you're right in noticing that SPX.XO and SP500.X are two symbols tracking the S&P 500 Cash price, with both updating every second. In terms of other symbols that refresh more frequently, it's worth noting that the frequency of updates can vary based on the data provider and the specific instrument being tracked.

While SP500.X includes Bid and Ask prices and updates every second, not all tradable instruments necessarily update tick by tick. Some assets may have a slightly longer refresh rate depending on the platform or exchange providing the data.