I can say from having a TE250 plated with MT21 tires as seen below...
Well, it was not terrible on the road. I had the same tires on my KTM 950 Super Enduro and it was great to 90mph (with a scotts steering stabilizer) before the tires started to feel like you were going to be in dangerous territory. As for the TE450, well I had my 07 TC450 up to 90mph on super hard packed alkalai flats (again with a stabilizer) and it was ok, doing regular speeds around town would be fine.
The problem you're going to run into is that any tire that's decent for the street comfort, gets good wear, doesn't want to wash out around corners or gravel, etc - you're going to HATE it on the dirt. And same with a tire that's good in the dirt is going to suck on the road. The MT21 is only half of each, so you end up with something that is moderately tolerable for street and sort of gets out of its own way on the dirt. Or you get two wheel sets with different tires on each and call it a day.
As for commuting it will not be fun. The oil
maintenance is like a race bike, I don't know about other people but I religiously change my oil every 4-6 engine hours. Then again I'm wringing it's neck off road most of the time. The seat is not comfortable, be prepared to wear padded shorts or have rattled off your own set of balls by the end of a solid hour of sitting on a thumper like this.
The TE610 is more likely what you want. It's more of a 60/40 bike like you are describing vs the TE250/450/510 bikes that are at most 40/60 road/dirt or 20/80 depending on tires.