for future reference, %intensity is normally based off your 1rep max. so if say you can bench 200lbs for 1 rep, then 60% intensity for 10 reps is 120lbs for 10 reps. there are also calculators that can guestimate what your 1rep max would be from your multirep bests.
Also, as a general rule in my workouts, after my first couple sets which i consider warmup sets so to speak, I always go to failure at whatever the rep range is. especially if it's under 8, and depending on how you're training i'll go past failure. for my bench for example, some weeks i do 1rep max singles, where i just work my way up about 25lbs below my 1 rep max and just keep adding 5lbs at a time, and try to beat it till the weight beats me. Other weeks I do 5x5. where for me for example my new 5 rep max is 225lbs. But I can only do that for like 2 sets tops before i'm so tired i'll need help (spotter assistance) finishing some reps for the last 3 sets. but thats fine, it forces my body to adapt and i'm seeing my 5 rep max increase about 5 lbs every couple weeks for the last while by always pushing to just beyond what my body can do.
to note though, i only really do this for like 1-2 movements in a workout. it just takes to much out of me if i do everything like this. so for example on my max effort push day, i'll do this for bench and sometimes for oly clean and press where i pull from the knees. for the other stuff like cable crossovers, incline bench, etc i'll do like 3x8-12 where i'm just hitting failure and not going past.
weak bis can be worked fine by not directly working them.. the bis assist back movements. more in some than others. so if you drop a bi isolation exercise, I recommend you add chinups, in which the bi is a big assister in addition to working the back effectively. if you can't do bodyweight chinups then find a cable machine that can give you weighted assistance and use that to help you.