Do the Sufferfest vids have power targets? The ones I've seen do not, they set effort targets, which is a very different thing. Without power readings, how can you evaluate effort? HR? Sure, but if you're pumping out RPMs, you can drive HR up without driving up power, and if you're not measuring HR with a monitor, then you're really just flying by the seat of your pants with regard to effort evaluation.
All of which is fine, but it's not a proper training program. It's not individually tailored, and there are no real metrics for evaluation, so really, the Sufferfest vids are just motivational tools. Again, that's fine, if it meets your goals. Just putting the time in trying to follow the videos is a good thing, and will definitely improve most folks' cycling (the main exception being, perhaps, those on a true training regimen).
As has been mentioned and suggested, it's probably a good idea to vary how you use the videos, some days focusing on hitting the cadence targets, and other days, focusing on rolling a bigger gear at below suggested RPM (e.g. when Sufferfest says go 100rpm, do 90).
Ultimately, as has also been mentioned already, you'll want to combine power and cadence to push up your baseline output at lower HR, which is the basic definition of improved fitness, i.e. more work for less effort, and even higher power at max effort.
Not knowing what tools you have to measure performance, I'll just say that the more data you have, the more meaningful you can make using the SFest videos. You'll be able to track progress, see improvements, and target deficit areas. Certainly modern training is all about the language of power, so a meter is the
#1 way to go if you want to approach this seriously. However, even estimated power, e.g. the $99 Cycleops Powercal, will allow you to start putting some more meaning to effort evaluation and tracking.