this is what I have for Grell. I just trimmed the bangs a little and spiked them with extra hold hairspray. There is a slightly shorter 40" long one called Athena that is a more manageable length but it requires more styling work.
If you are not used to long wigs I would not go longer than 40", especially if you are wearing it around all day long at a con and do not have a helper or a way to stop and brush it out.
A good way to wear those 50" knee length styles is to trim two long side pieces a bit shorter, like waist length and keep them at the front smoothed with hairspray,, and tie the rest back in a low ponytail with a ribbon,, and only take it out when you are doing a photoshoot. It lets people know you have the long wig and looks ok from a front view while still keeping it easy to wear.
if you join epiccosplays facebook page they'll let you know when there are sales coming up. sometimes there's free shipping and other promotions. they also often have booths at cons so you can save money picking up your wig that way too.