On the admin UI, the System menu column as of recent contains some really powerful and helpful pages.

System > Throttling – lets you slow down delivery, in order to slowly warm up your new IPs first. Freshly re-designed for better readability.

System > Speeds – see the current speeds per target, range or message id.

System > SMTP Charts – see what the targets are saying.

System > Deferrals – if you have expired drops you can see here what happened.

Now you can use the web UI to shape your traffic, while keeping an eye on the feedback. As ever, the red Help button top-right gets you the pertinent help page.