First of all, data quality depends on the edge you want to test. If you want to test intraday, you'll most likely need tick data and these are expensive. Minute data does not work because it depends on the data collector how the minute is defined and which data is included in a period.
EoD doesn't matter that much, margin of error can be larger.
You most likely need to setup your own database and compare it to the data you bought from an external source. If you have more ticks than external datasource the data you bought might be filtered or snapshotted.
Competitive data will always be collected from a direct exchange connection, never from a broker or data provider, especially intraday. It's a ton of work and really expensive, which is why everything on intraday basis is dominated by larger shops. You have no chance doing that as retail with retail platforms.
If your edge is 20cts on average and you obtained data from IB which is a snapshot of SIP, you can asume that you have no edge at all because you only tested on 2/3s of the ticks that actually happened on exchange.
right, so go do it and tell us the answer. Otherwise blah blah blah
