Well the fact that the 2 into 1 wont work is not ruled out in my mind yet. We have a 460cc 6mm cheetah motor running pro circuits with a 2 into 1 intake and a 38mm lectron on it. It made 92 hp on the crank dyno last weekend. It had a very nice looking torque curve also. Currently I took my carb off and saw some small flaws and mismatches inside my 2 into 1 intake, and I am in the process of cleaning it up. I got out the porting tools yesterday and started match porting it to my reed cages and even took a little material off the rubber boot. The inside of the intake has some cnc cuts that can also be smoothed out to help increase the intakes capable volume and general flow characteristics.
If you want to do a dune port and would like a mid-top powerband then some good pipes to look at are the T5, SST (FMF), and supposedly?????? the Paul Turner mid-tops???? Now I dont know how the PTR mid-top pipes do, but we have a set of PTR midrangess on a 4 mill and it made power to 10,500 rpm. My Banshee with a 2 into 1 pipe makes power till 9k rpm. However, on that 460cc 6mill cheetah motor the PTR mids made 5 less hp than the pro circuits. So it is going to depend on your stroke, porting, compression, and the match up of all your parts. I tell you what though, I do a lot of bottom end type power stuff for the guys we ride with. It's priceless seeing the look on someones face when they ride their bike the first time. It almost bucks them off cause the bottom end acceleration is phenomenal.