I swapped my M695 for an ST2. At around 100 pounds lighter, I found the Monster was definitely more flickable through the twisties. The better suspension on the ST coupled with adjustable ride height helped narrow the gap a bit, though...
Been away for a couple weeks, so just responding to a few thoughts now.
The ST4's added weight is definitely more noticeable to me and it's also a little more top heavy, compared to the monster. Suspension wise 01 monster 900 suspension was the same as the ST4, but I've upgraded my monster to SBK forks and an Ohlins rear shock, which certainly makes a difference. While I did upgrade the wheels on the ST4 to ST4s wheels, the monster has Marvic mag wheels, so there's no advantage for the ST there either. I've also put upright handlebars on my ST4, but it's still a longer reach to the bars so the monster is more comfortable that way as well.
I actually just found a set of hard bags and racks locally, for the monster, so I'm gonna spiffy up the ST4 and throw her up for sale.
The ST4 is a great bike and I do really like it alot, but every time I'm on it, I wish I were on the monster. I get stressed having more than one motorcycle as I'd much rather be out riding than cleaning and maintaining. I've become a bit of a minimalist in my old age and one monster fits that mindset perfectly. The biggest reason I bought the ST4 in the first place was for 2-up rides with my woman. Once I get the hard bags set up, we can tour 2-up with much more room.