First and foremost, Eva recently demonstrated the ability to move and fight at a very high level even while mid-incantation. She was surrounded and attacked by three opponents trying to interrupt her spell, each of these three being quite powerful individually. She beats them all down without having to restart her incantation. Shown here:
http://www.mangafox.com/manga/mahou_sensei_negima/v36/c332/7.html
http://www.mangafox.com/manga/mahou_sensei_negima/v36/c332/8.html
http://www.mangafox.com/manga/mahou_sensei_negima/v36/c332/9.html
Feel free to ignore the stuff with the other classmates. It's unrelated.
As for raw power, her attack from a much earlier fight is still probably her best showing. Unfortunately we don't really have much of a read on her upper limit because her power is sealed most of the time. When it's not sealed she stomps with little effort, so the extent of her power is unclear. Anyway, here's probably the best we've seen:
http://www.mangafox.com/manga/mahou_sensei_negima/v06/c051/16.html
http://www.mangafox.com/manga/mahou_sensei_negima/v06/c051/17.html
Taken together, I can see her having a shot here. She's gone straight for the big spell both times she's actually fought at full power, so that's not going to be an issue. And even if Megas withstands her magic, the pilots might not be so lucky. They could very well end up frozen solid inside the machine.
As an aside, as may be apparent, the other time she fought at full strength was during the first feat I listed. The spell she's chanting there actually goes off starting here:
http://www.mangafox.com/manga/mahou_sensei_negima/v36/c333/6.html
It's not directly applicable because it was specifically made to seek out entities like the ones they were fighting at the time. Does potentially give another example of the level of her ability though, I guess.
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