You could try 5.1g rollers, i like them a lot. Your will lose some top end tho. Now i only get around 41-42mph in flats but acceleration and uphills is good for me. I got a couple of long steep hills on my way to work, used to drop to near 20mph on stock set up but now it only goes down to 30/31/32mph,even accelerates up a lot of hills, mine never drops under 30mph unless i hit a monster hill. Saying that o never really dropped under 30mph even on the 5.5g's.
I shaved 1.2mm off my drive boss too which gave me better top speed, now its at 36.8mm instead of stock 38mm. The Malossi oit comes with a 37.5mm boss i believe.
Maybe buy a cheap tach off fleabay to see how the revs perform on the hills, mine was a tenner from the US. You really need to keep the rpm over 6500, closer to 7000-7200rpm really.