I'll tell you, Pablo, your efforts to upgrade the accessories for these kits is just great.
I sure do hope it all works out for you.
I'm certain to order something from you. And it might not take a long time. The air filter will probably be first. I'm considering the shift kit, but I'm not positive that I actually want it. But if the answer ever becomes yes, then I'll go for it. Maybe you'll have other stuff to choose by that time, too. I hope so.
I will say, if you really have everything else with your engine well dialed in, the advantages are moving the spark away from the hole recess, centering the spark in the chamber, less prone to fouling (allowing for a touch more oil), slight increase in compression ratio, naturally a tad cooler running than the B5/6HS because of the larger mass and more thermal transfer path - yet hotter tip because of the linear distance.
We got a load of BP6HS plugs in, but they were the same price as our standard plugs, just more of them. Then guess what, a butt load more show up - 2X the shipment. Rather than ship them back, I said we would take them if our supplier knocked the price down - which they did, a bit.
So ala Trader Joe's we pass the savings on to you. $2.79 each.