I would go this way. It's probably the fastest route (BA SFO-LHR-DME could be a bit faster, though). The JFK-HEL plane will be a new A333 with a quite decent business class product. AY's European business class is among the best, and for that one and half hour flight perfectly comfortable, even though you have the same seats as in coach (but with the middle seat blocked).

There at least used to be lots and lots of Russians on the JFK flight so they have mastered the connection drill in HEL - it will be very efficient and beat LHR hands down.

The bad part is flying to SVO which is an inferior airport to DME.