One thing I've railed about since the day I got the B4, is parts availability.
Now, a lot of the parts that we can use come off the GS500, GSXR600 - 750, and even the SV650s.
NONE are ever in stock at the dealers, and the word I usually get from them is that it will have to come from Japan. 6 -8 weeks is usually the optimistic estimate. Now this could be just Suzuki Canada being incompetent, as I have gotten parts out of Suzuki US, via Bike Bandit faster, but it is worth considering availability.
The SV is a twin, IIRC, so it will be somewhat different than you're used to in power and maintenance.
According to wikipedia, the 2003 and up SVs are FI. That would be a really good thing to consider. The difference between the carbs on the B4 and the FI on the 919 is night and day. I hate the B4s carbs. (love the bike, hate her breathing apparatus.) The 919, I just start it up and go. Bliss.
That said, if I've ever had to order a part for the 919, it's been no more than 2 days away.
It's a "retuned" version of the CBR900 fireblade engine of a couple of years back. It can be tuned to make more power than it does currently with a power commander. (106HP and 65 ft/lb of torque as dynoed.) It's a strong torquey engine, that you can lug along, or you can be all manner of hooligan on. (In fact, that's a large part of the reason the other half doesn't like to ride it. He finds himself being a hooligan on the bike too much and prefers to not have the option.) Because the bike makes it's power down low, you can be cruising at 120kph and barely feel it in the engine. (Not so good in a 50kph zone.) There are a number of parts that the 919 can share with the CBR900, 929, and 954.
And there are a few good forums for the Fireblades.
Now,.. here's another kicker. What's the insurance cost on the SV650? I suspect that it's classed with the 600s, which means it could be a god awful kick in the pants every year for anything other than 3rd party liability. At least here, the 919 hasn't hit the radar yet. The SV was going to cost me about 1/3 more than the 919.
My vote is for a 919. Best to find one used, then the price isn't that bad, or find a dealer with a leftover 2006. I've sat on the SV650, and it felt ok to me, but there was something I liked better on the 919. I can't put my finger on what it is, but it's more comfortable to me than the SV, and that's important on a long run.