Training and Cadence Variances

I’m new to TR and will be doing Leadville this August. I have primarily a running background but have done numerous triathlons over the years (including IM distances). I did the ramp test a few weeks back and my FTP was estimated at 245 (3.38 FTP/kg). I’m training on a full suspension MTB and a Yahoo Kickr. Historically my riding cadence has been around 90 +/-. During most of my TR workouts, I am able to maintain the similar cadence. However, as my workout have intensified and today (for example), I did Palisade which alternated between 95% to 105% of my FTP, my cadence drops to around 60. If I am able to complete the workout, but at a much lower cadence during the intense intervals, is that still beneficial or should I reduce the intensity so that I am able to maintain a higher cadence of 85 +/- during the interval? Given that my “A” race is Leadville which will consist of a lot of climbing, probably at a lower cadence, does it make sense to continue to grind it out? I don’t have any issues with my knees. Thanks.