welcome aboard !
i have had some trouble with mine as some here know.lol. had starting issues from brand new, turns out that the decompression valve spring wasn't installed right. all looks good so far since they found the problem and i'm happy now. LOL. but other than that i love it.
now, if you are torn between the 700 and 550, i would go for the 700 regardless on how fast you cruise at. i look at it this way, the 700 has more displacement, more power....equals to less strain on the engine no matter what you do with it, especially if you want to plow snow with it. but that's just my opinion, go with what you desire most.