if you're thinking about using miles...there are a few options. You could use Czech airlines (Skyteam) member through JFK/Prague to get to Kiev. Or even Air France through Paris. You would have to call NW directly.
AH...you ask about the perksaver and perkpass..If Perksaver is not available..it'll just show perkpass. There's no way to select just perkpass i don't' think...it's defaulted to search just that. You might use the calender to see what dates are available. Note that the calendar is not always accurate.
In Y (Coach) perksaver is 50K RT perkpass is 100K.
Using miles to Europe during summer in one word is-DIFFICULT. You have to plan way ahead...like 360 days when they release the award seats.
If you're planning to use a website to help you find award tickets...my personal choice would be
expertflyer.com...do a search through the threads and you'll find more info about it.