I don't think we're likely to be seeing any real difference in engine modes from the teams. It's not like it used to be where they had a dozen engine modes they could choose on the fly, and Merc had a special quali mode they'd only roll out for those few laps. Everyone will want to get the best data out of practice and everyone will want to spare the engines if they can. Since everyone is in the same boat, I don't see there being a great deal of incentive for particular teams to hide or show pace.
As
@jaybee says, it's not like they're giving anything away to the other teams when everyone gets their tape measures out tomorrow anyway.
That doesn't mean practice is a straight reflection - teams will still have been running different programmes, etc.