Hi!  It just so happens that about this time last week, I asked about an extreme "rattle", as I called it, every time I passed 50mph.  Maybe it's the same problem you have.  
Several replies suggested tightening the 3 speedometer mounting screws.
You have to remove the gas tank to get to them on its underside.  They said it was easy to do.  If you've never done this before, here's what I found on my '99 Savage.
After you remove the seat and the screws under the seat holding the tank to the frame, disconnect the rubber hose to the fuel valve and the small rubber spring-covered hose directly behind it.  
Plus, loosen the speedometer connector (nut at bottom of larger spring covered tubing on the right side of the bike).  
Now you can get the tank loose to get to its underside.  You might hit a snag when the fuel valve wants to jam up against a rigid brass tube, but when I called a mechanic at our Suzuki dealer, he said to wrestle it any way I needed to in order to get the tank loose.  
I found only 1 of the 3 screws loose, but tightening it made a noticeable difference.
I also found that putting it back together was a lot easier than getting it apart.  
Hint: A second person to hold the tank while tightening the screws would have been handy.  
Good luck from this "Lady Rider"
dunk

The local dealer said people were returning Savages because of excessive vibration, and I thought "well, DUH!  It's a Thumper!"  When I got Thumper I was rather surprised at the low level of vibration -- Suzuki did a great job on counterbalancing.  Then I ran my finger thru the table saw and for a couple of months I could not allow that finger to touch Thumper -- the vibrations *HURT*.

What you need to do is swap Savages with someone to see how each other bike behaves.

You said that the few hundred miles you have so far have been below 45 mph around town.  Now you get up to 55+ and the vibration concerns you.  

*Note:  This is entirely NORMAL for a big single.  Spend some time on the highway and get acquainted with the way the bike runs and handles.  You are just fine...ride and enjoy.

I appreciate the replies.
No Way am I getting rid of it!! Never crossed my mind!! I understand there is going to be vibration and have gotten used to it around town. I love to be sitting at a stop light and watch the mirrors shake!
It didn't seem like a little buzz in the bars. It was more than that. It was like holding on to a 652cc weedeater!!
I'll try it again on a longer stretch to diagnose a little better.
I have been thinking of the grips 911radioman put on his. They make a new version with flames that would match the bike better but don't look as cushy.
Also there are NO WEIGHTS on the front wheel and a HUGE ONE on the back. Could be the front one EH?

I'm  going to have it checked at the dealer this week. Too bad there isn't anyone close I know with an S40 for comparison.

And, just to throw in another interesting, and somewhat weird, point into the vibration discussion...

Ever since I put the apes on the savage...I don't notice the vibration as bad in the handgrips.  I was warned by a lot of people that the vibration would be worse...but now I don't even notice it, whereas before it would be enough to annoy me.  And no, I'm not even going to try to explain it.

The only really noticeable vibration/wobble I had was within the first couple hundred miles, and it worsened each time out over 50mph, in the front end.  Ended up being a loose pinch bolt on the front wheel ,  dang teenage assemblers at the stealership!!