I use manual clutch and shifts with a G25 in road cars only. In GTR class and UFR/XFR and alla single seaters, I use auto clutch and sequential gears, since they are supposed to be like that in real life too. I think these cars (and especially GTRs and single seaters) should allow clutchless shifting even with manual clutch enabled, since they are supposed to use sequential gearboxes...
P.S. I use left foot brake and rev up for downshifting without a clutch in road cars, but I have the foot ready for clutch too, if the gear isn't selected after all. A little bit risky, especially with some cars which need the revs matched exactly before they take the gear in.