I keep adding my 2 cents to old threads but hey, everyone needs a hobby... anyway, with a bike that clocks in at just about 400 kilos without rider, you want a sturdy front for braking duties. Grip is the same even with a bicycle tire, but if you put that on an R3T it would shred for other reasons. Feel while steering is just one factor, but another is how well it can handle getting most of the weight of the bike and rider on it when braking hard; a 150 should deform considerably less than a 130 under such circumstances and possibly give more predictable grip, and I don't think Triumph picked the 150 size out of a hat.