Did watch tape on Shevchenko and Pena. Not sure why this line is even, I dropped ~5u on Shevchenko at once and might even go bigger if I have time to do some additional research regarding training and such.
Shev is far, far ahead standing, has a very good clinch game and survived a round on the bottom against Nunes who except for that fight have four straight r1 finishes against Tate, Rousey and McMann. If Nunes can't finish you with a round on top while fresh Pena sure as shit will have issues with it too. She also looked fairly fresh in round 3 against Nunes, had no cardio issues going five against Holm at a half decent pace and always looks fairly relaxed in the cage not using a ton of energy.
In short, Shev has done much better then anyone else the last few years against Nunes and owned a former Strikeforce (on short notice) and a former UFC champion in her last 3.
Pena on the other hand has a good win over Zingano, which is very impressive although I think Zingano gased fairly badly in that fight and did some dumb shit, but other then that she has wins over Jessica "1-5 since 2014" Eye in a fight where she gave up a round to Eye's "dominant" grappling, Milana Dudieva and Jessica "1-5" Rakoczy (who in her defense is much better then her record suggest, but on the other hand also capable of making 115).
Before that run she did well on TUF, beating monsters like over the hill Baszler, Sarah Moras and some chick I never even heard of and I'm borderline autistic with names. I don't want to go back even further since that would be more then 3 years, but let's just say it doesn't get better.
Lastly, I'm not even sure Pena is a better grappler. She probably is, but I wouldn't bet her at -500 in a pure grappling match and if it goes to the ground Shev might very well have top position for the most part due to her clinch game.