I'm a 4a with fine to medium strands; my hair is very dense. My hair grows about 1/2 inch a month give or take. Once I found out about moisturizing, PS and low-manipulation, I haven't had any problems with retention.
My hair is pretty thick. For some reason my 4's seem to grow slower than my 3's but actually the 4's are just really coiled. And they seem stronger than my 3's.