If you look at the GWR pocket timetables here -
https://www.gwr.com/plan-journey/train-times - a good guide to the odds of seeing a Turbo on things like London-Oxford services is to look for services that do not have a big black blob at the top of the column - the blob basically means the train is booked to be an IET or HST.
Paddington-Bedwyn, Reading-Basingstoke and services starting at Reading for Newbury/Bedwyn are all Turbos - bar I think an HST on a fill-in turn from Paddington to Newbury and back just after the morning peak but that may not run on Monday anyway as it's a bank holiday.
And a word of warning to anyone hoping to get a train to Worcester - whether with GWR or WMR - from Saturday until next Wednesday - a bridge over the Worcester bypass is being replaced to allow for road widening, so best to take a look at what's going on here
https://www.gwr.com/travel-updates/planned-engineering/cotswolds2018
Worcester-Hereford is also shut over the weekend.