This really gives some great insight into how effective RPE is for training doesn't it?
Obviously watts is watts, and what you feel is perception. 275 on the trainer is no harder than on the tarmac, but you probably perceive the two differently because you are more comfortable on the road than on the trainer. If you road the trainer more, you would likely start to feel that the workout was no harder indoors (not that you really want to this time of year though).
Just to clarify though...we are talking about the same power measurement device and the same metric, right? If you are using average power on the road vs actually holding the power for the entire interval on the trainer there is your answer right there. Also do not make the mistake of thinking that two different PMs are properly calibrated/accurate/precise unless you have verified it yourself.
My heart also perceives that it`s harder indoors, i.e. my heart rates is in the "right place", but the watt numbers are lower than outdoors.
When the power dropped at around 1:21-1:22, i considered quitting, before making a last effort.