I bought a 3.1 IMS awhile back. I've had no problems, it mounted easy and doesn't make it any more difficult than the stock tank with regards to removal and unplugging the pump. The stock tank was just too small with my daily use. The IMS has made it much more manageable for the day to day work. I did get the Wolfman rack setup w/ a rotopax for that extra gallon if I ever need to use it.
You just need to look at what use you have for the bike. Will a large tank be better for your typical day or would something just a bit bigger than stock suffice? Only you can answer that.
WR250R - perhaps the ideal motorcycle for myself
Throw in a passenger and I'm unsure of what I'd consider ideal. Maybe a Multi?
I am now for sure sold on the Dual Sport style bike.
Keeping the Vulcan for now. The ladies seem to love it.