Rocket would probably be the wrong word to use, but given that Big Brother has in the past seen a high of nearly 6 million viewers and, the average for series 11 (just gone) was 2.5 million it would seem that Five could anticipate a pleasant increase. Some of their major shows have only managed to reach 1.5 million and so even ratings of 2.5 million would be a big step for Five.
It might not be enough for C4, but it would increase ratings, albeit not massively, elsewhere.
Edit; saw your post following Mathew's after posting (started writing beforehand). Fair points, just seemed like in the above post you were refusing to acknowledge it would positively affect their ratings at all.