How you use your heep is going to make a big dfference on which is best. I regeared my heep and don't see the need for a bigger/heavier motor so for me thats all I needed, but I don't see allot of street use and I keep it as light as possible. If you see allot of street use then looking at the motor swap would be more usefull, possibly even w/ the gears. And as much as I hate to see a chebby motor going into a heep, the 4.3 is a good choice for a balance between weight and power.
I guess what my suggestion boils down to, do the gears first, if that makes you happy your good, if not swap the 4.3 in.