Low cadence FTP test for specific block?

Hey Guys

In the next few weeks I will be doing tempo rides as per Tim Cusick’s advise (75 rpm) and Sweetspot at between 50 - 70rpm (Tom Bell, High North). I have a race later in the year with a 50km climb. Most of the climb is 2-3% but there are 3 sections for a few km that are 7-9% in gradient.

I have a dumb trainer and in order for me to execute these intervals I am just going to stick it into big ring and find a cadence that fits the above.

The problem is I generate much more power climbing or at low cadences than at where I normally spin at (95 rpm+). I figured I should probably do a “climbing” ftp test tomorrow to make sure I am hitting the correct zones.

Would I be correct that for the FTP test I should just drop my bike into the largest gear I can muster 53-12 or 11) and then execute my ftp test?