Between a 6 speed gear set prob an S-E type or a oil cooler.I know most people say you dont need a cooler especially if you run synthetic oil.Some say you don't need the extra gear depending on what type of driving you do.I am leaning towards the 6.I know the price difference is big I just want to see what others say.I have a 06 Train with a GMR 98 KIT.
My wife has an 06 Dyna with a 6 speed, and it's great. But I don't think it's worth better than 10% of the cost of the bike. You can buy a lot of "stuff" for the cost of that gear set.
I would think that with the Cost of the gear, and the cheapness of the Cooler compared you would do both. Why spend the money for the gear and not the Cooler?
I have the 6th gear in my 07 Low Rider. I haven't put the brake in miles on it yet but I don't see me using it much. If you live in a hot climate I'd go with the oil cooler.....Then again I already have the 6th gear.[8D]