Dos circuit is basically a proma copy but actually a little better silencer.
I had to crunch some numbers myself because something seems off, I'm running 15*40 on an e50 with the airsal 44, bing, proma GP and topping out at 45=9000 ish rpm. If anything my gears are a little bit too tall, it was good at 14*40 but I didn't like how buzzy it was at top speed.
You should be going a bit faster barring dragging brakes, bad bearings, etc. That pipe should hit peak power around 8k, and you want to be geared so you rev a little past peak power so as you slow down, your bike digs into the power band and doesn't slow down as much.
My original advice a few months ago was to gear that setup for 8500 at top speed, that works out to 18*35 (assuming you have a 2hp engine) that will probably get you the highest top speed and the best accel. That kit should have no problem pulling those gears.
But seriously, if you like it the way it is, nothing saying you need to screw with it. It's just fine and will run for ever the way it's set up now. I highly doubt the carb will help much, it's just too much gear. Since you probably have the 18 (stock) and wouldn't have to break the chain to swap, it might be worth a try just to see if you like it better.