If it feels fast it probably is!

You can feel the boat slow if you dig the bow in hard. You can also feel the boat slow if it does a lot of hobby-horsing - which happens more if you stand back.

There is a rule of thumb I've heard that when a hull is more than 6 times longer than it is wide then the waterline length becomes less of a factor in limiting speed. That's why the Moths evolved down to 250mm wide before they moved on to foils. So for a Mozzie, yes that extra little bit of waterline length will help, but other effects are more important.
Try to keep the boat steady so the sail(s) can keep driving hard, and don't let the transom drag.

I've never seen markers on the bow of a Mosquito.