I would choose between the 4sp OD gear set or T56 Magnum. The TKOs are not worth cutting the car up.
Silver Sport 6sp kit is nice but after you add bell, hyd setup and clutch to the base kit you are over $6k.
Passon gear set is $2K if you have a 4sp car.
So is a modern designed trans with 2 extra gears worth $4k more?
Your going to cut the floor with either a TKO or T56 regardless if you want it to fit/clearance correctly, and achieve YOUR desired/needed driveline angle, for some the trade off of cutting the floor is no issuse, for those that have issues with cutting the floor there's other alternatives...
but for those that have a build that's going to see some stout rear gearing, a deep OD 5 spd or double OD 6th gear is the only way to go...
As to your question: "So is a modern designed trans with 2 extra gears worth $4K more", look at it this way, if I told you I could add 250+ hp to your current engine build for $4K more you'd be looking to round up some cash, same as if I told you your .80 gear set 4spd OD for $2K running a 28" tire and 4:10 gearing will be turning 2500 RPM at 70 mph or 5000 RPM at 130mph, you might be OK with that?, but if I told you for $4K more that same tire/rear gear set with a T56 .50 OD can still turn 2500 RPM but your cruise speed is now 110 MPH, and at 5000 RPM you have a 205 MPH capability, I think you would be inclined to spend the extra $4K, unless you don't like going fast?
