Moves on paper tips/news tend to unwind through the course of the day but things are a little bit different here. I mean even if the papers aren't 100% right they aren't 100% wrong. I'm fairly convinced now that there's an auction going on so it's just a matter of what sort of deal can be squeezed out.
Midway have had a good share price run lately iirc so I can imagine that they'd like to do a deal with a good proportion of paper. But, not being as attractive as cash, they would have to offer more than somebody who was offering a high proportion of cash.
There is a sniff of truth about it although £600m+ does seem a bit high.
I guess though that given SCi have done two of the best bits of M&A I have ever seen (buying Pivotal and Eidos for peanuts) maybe they'll score a hatrick and sell the company for a stonkingly overvalued amount.