I'll vote for 7c for BBB.
I don't think it is harder than other Orme 7c routes such as Body Torque Direct or Tomorrow People.
I actually found Martha (the 7c direct on Night Glue) harder... probably due to climbing it in a heat wave though!
I though Parasite was harder than Mussel Beach, but still at the easier end of 8a. I think it suits bouldering fitness more than the longer 8as to the right. Contrary to what the guide books says, Parasite is a very good route and it's good to see it finally getting some traffic. Until this year, I have never seen chalk on it.