What you need to look at is the top tube length. Since you said that you are "quite cramped" on your Sekai, measure its TT length and then add about 2cm. Next, find the Windsor size that has a similar TT length. Clearly, standover won't be an issue with your relatively long legs. Nonetheless, it's quite difficult for me or anyone else to help you with sizing given the limited info you've provided, since we have no idea what your preferred riding position is or the type of bars you are using.