Hi Ronin369, yes you made me look
OK here is my opinion, of course I could be wrong.
Don't underestimate 70 BMWs, I know how they handle because I own one. (R76/6 1975) They can be ridden really hard until the valve covers touch the ground if the tarmac is perfect.
Almost all of them have the same shocks at the rear by now, and they re Koni Dial a Rides, they re good enough. Their handling is almost not affected at all by riding with a passenger, so this isn't a factor here.
In any case if the BMW went through the curve with no problem, you certainly shouldn't have a problem either on your SV, even with soft fork etc.
So, I think you should look elsewhere for the answer to the problem.
Did you have the same line going in the turn?
There is no way that I know of, that going too slow will make you hit the brakes in a turn... You mention that maybe your fork dived too much and that maybe that was that made you 'stand up the bike and hit the brakes'.
In reality it usually goes the other way round. Think of the situation again in your mind. Could it be that you were still braking while going in the turn, thus making your fork dive, felt unsafe and then hit the brakes harder, which made the bike stand up and run over the yellow line?
Maybe your friend is more experienced than you, rides his BMW for many years and knows what to expect from it, or maybe he knew that particular bend an dwas prepared for it. Or maybe I'm wrong
But it's worth considering what you really did, because the SV really has superior handling than the BMW, except if you also had a passenger.
Could it be that because of the low speed you got yourself countesteering into the bend although the speed was too low for that?
I think you could have saved it by just letting the brakes and lean the bike to take the turn. The BMW has more weight and a 100/90 -19 front tire, your SV has a 120/60 17 front (if I'm not mistaken) so the contact patch on the SV is slightly bigger for much less weight also.