Sendy can only send as fast as the mail host allows. To be honest, I would use the Amazon SES setup in Sendy for your email, that way your host has nothing to do with it, no limits. You will get better inbox rates with SES than using your server IP. Chances are, you may do a lot of damage to your IP sending that sort of mail, because as people hit spam or such on your mail, that IP is being logged and smashed as a spam source. It isn't worth it.
I've had the same IP for a lot of years now, and just having members decide to leave and hit spam on their mail client for all their chosen subscriptions when received at their inbox... that has all added up that I was starting to get signup messages and such going to spam too much... so I moved my entire site to SES, 99.99% inbox delivery once again.
You're better off allowing a professional to manage email IP's nowadays... SES allows this very cheaply.