I'm sorry to hear about Speedboat's heart murmur.
Did your vet tell you what grade his murmur is? They're rated on a scale of 1-6 depending on the severity. Heart murmurs in cats can be indicative of an underlying heart problem, however often the cause can't be identified and the cats live a normal, healthy life regardless.
With my male cat, Peter, who just turned 3, my vet detected a grade 2 murmur for the time when he was 9-months-old. After hearing the murmur on two more ocassions and taking xrays which showed that Pete had a slightly enlarged heart, he was referred for a cardiac ultrasound. My vet originally pushed me to take Pete to a feline cardiologist, which would have cost between $500-600. Instead, based on a friend's recommendation, I took Pete to an internist who specializes in feline cardiology, which cost less than half. It was definitely the right thing to do because Pete was diagnosed with HCM (Hypertrophic Cardiomyopathy - a gradual thickening of the walls of the heart). Since we caught it early and Pete is young his prognosis is good, although there is no cure. The good news is that it's very mild at this point. Pete takes 1/2 a baby aspirin twice a week to keep his blood thin, and a low dosage of a beta blocker daily to regulate his blood pressure and prevent blood clots. This is mostly preventative for now, but seems to be working because his last ultrasound (he has them annually for now), there had been no further progression of the disease.
Anyway, that's my experience. Hope it helps and that everything works out for Speedboat. Feel free to PM me if you want to talk.