I've only flown Y class on Finnair as well, just travelled the JFK-HEL-JFK sector this summer actually. All of the MD-11's have been outfitted with the updated C class setup (28 seats). Just try not to get an "E" seat as much as possible, you've got one person on either side of you in the middle of the plane. You can reserve a seat up to 6 months prior to the day of departure.
The seats are very nice (I toured OH-LGA while it was turning around at SFO in 1999, and grabbed a quick feel for the seats
), they have a 50" seat pitch (according to airlinequality.com), with noise cancelling headphones and a 13.9in. PTV that comes out of your armrest. The PTV has 12 channels of video and a further 18 of audio, and also includes several games as well. Airshow is available on Channel 12 of the video menu. There is also a satellite phone available at each seat, the charge is only $3.50 per 30 seconds (minimum charge for 1 minute, or $7.00) There is also the possiblity to send faxes, the charge is $3.50, and is sent from the pursers station (rear of the left side of the C cabin).
I've heard lots of positive stuff about the C class, hopefully I'll be able to try it sometime! Enjoy your trip!
Head in the clouds... yet feet planted firmly on the ground.