Mine's not the extended, so my opinion may not be what you're looking for. But the extended model is only 16 inches longer than the regular model Interstate, all of that in the rear overhang. Wheelbase is the same, and so is handling between the two Interstates. An extra 16 inches of length adds almost nothing to your tail-swing.
In terms of handling, the Interstate is almost exactly comparable to a Chevy Siverado 2500 Crew Cab Long Bed Pickup. Interstate wheelbase is 170 inches; Chevy 2500 is 167 inches. Interstate turning circle is 55 feet. Same as the Chevy 2500. As long as you're mindful of the 9'8" height of the Interstate, anywhere you can drive a big pickup, you can drive the Interstate, with no problems at all.
The key to taking the Interstate around a tight right-hand turn without bumping over the curb is the same as for any other big vehicle; wait until the rear tires are at the tangent point between straight and curve, then crank the wheel over. You should probably take the turns a little slower than you're used to, at first, until you develop a feel for exactly how much clearance you need.
I thought getting old would take longer!