Hello Sandi,
We wouldn't recommend setting anything higher than 20 at a go because even though sendgrid can send more, if you do intend to send more e-mails within a specific threshold, some mail servers would flag your transactional e-mails as spam.
Anyway, what you can do is to edit the file /components/com_easyblog/services/cron.php and locate the code below at line 22,
[gist]
$result['emails'] = EB::mailer()->dispatch();
[/gist]
Replace it with,
[gist]
$result['emails'] = EB::mailer()->dispatch(50);
[/gist]
Replace 50 with your desired number of e-mails.