If you have access to an indoor smart trainer, it would be interesting to see how your road number compares to what a 30 minute or ramp type FTP test would come up with.
On Zwift, the climb up Alpe de Huez clone Alpe de Zwift takes me more than an hour and I usually end up averaging pretty close to what the FTP test (done on Zwift) said - usually within a few percent either way.
A couple of years ago I did the Logan Pass climb on Going to the Sun Road in Glacier National Park - something like 11 miles at 6%. That was my one opportunity for an on road test but it was on a rental bike and I hadn't even brought a heart rate monitor let alone had a power meter.