Has anyone gone big bore, but kept the bike otherwise stock?

Curious if anyone has done the Thumperracing or Athena kit and left the exhaust & airbox alone? Do you see any gains, or do you really need to uncork this thing if you go big bore? I love quietness, but would love a little more juice out of this scooter.

Im sure it would gain a lil bit on bottom to mid. Top end though wouldn't get that much of a boost because in completely stock form its choked on the top end by that little flapper and the exhaust. At least do the flapper mod.
What about the tubo kit? its not that much more than a big bore kit and would probably be easier to keep it quiet with other than the turbo spool sound.

I modded the exhaust /intake and used the powercommander tuner. then a year later did the 290 and downloaded a few different powercommander maps. Then I wanted it quieter so I put on the stock exhaust. I was pretty surprised that the 290 with stock exhaust made the bike so close to what it should have been in the first place. If i had it to do all over again I'd probably leave it stock except for the 290. Now long term reliability with the 290 is in question as far as i'm concerned and my values about just using the bike vs trying to make it something its not are not everyones values.
now days I just stay in 5th or 6th down to a 30mph corner and just lug out of it. back in the 250 days that wouldn't work,, it would just lug along and not gain speed.. it works much more like a 650 class bike now,, not exactly but closer than I thought it would.