Pinned in Zone 5

I’ve been following 80/20 religiously for two years and have had great results with my running. I typically run about 22 days a months and bike another 8, following the same 80/20 conventions on the bike. My HR zones are very different in the two activities as determined by Joe Friel’s 30 minute Lactate Threshold tests. The differences are very consistent across disciplines.

My runs and training rides are all very HR Zone compliant.

However, when racing my bike in a cyclocross event, as I did again last night, I stay pinned in Zone 5. In a 28 minute race, I spent 20 minutes in Z5, 5:30 in Z4 and the other three minutes in Z1-Z3.

Obviously, I am not recovering well from the bursts into Z5. My question is, should I try to keep my HR limit within Z4 for the first few laps and then max it out for the last lap? I have to think that 20+ minutes in Z5 is not a good thing and I’m probably churning away with sub-optimal efficiency. Yet… I could still do it and bested my previous time.

Obviously I need to be on the bike more frequently, build that sport-specific base, and focus on recovering from short bursts into a sustainable aerobic range. And I plan on doing this.

Again, my question is on race management. Is it best to stay in reasonable Z4 until the end, or can I just let it fly and make the best of redlining Z5?

Thanks in advance