The difference between 4-sp and 5-sp transmissions is about the same.  What you want to do is swap out the belt for a chain.

Yes, top end on 4speed or 5speed is about the same.
either swap the belt for a chain or look for a 16" wheel.
a 25" diameter tire will give 10% more.

But, really, I and many others go 70 from beginning to end of our commutes.  And then there's stinger who goes all day at 70.  With no issues.  A well tuned bike can do it.  Your 87 should have a 155 main so there shouldn't be a problem with lean overheat.  Make sure she's full of oil, keep her fins clean and don't stop suddenly or she'll over heat.

So why do you say she doesn't like 70?

yes.... 'yes officer, it said 65'  but you'll be doing 70

sounds like you got the head plug leak.

the kler wrote on 09/18/10 at 20:42:49:


You are pushing it "pretty" hard at 70mph but she'll do it and keep doing longer than your a$$ will hold out. Listed Top speed is 87mph. I'm assuming this is top cruising speed because I and many others have gotten stock machines to (indicated) 100 mph but Im sure I can speak for the others when I say 70/75 to 100 took forever.  If you're in top gear you're pushing it 70% of max. This aint a speed demon. Even with a lot of mods it's best at smoking everything 0-60.
Chain conversion really helps a lot. The belts are awesome. Whole time I kept the belt I didnt need to adjust it or do anything at all to it. It'd sqeek for a minute if it was rainy out but after it got going it would stop. Other than that it was great. But Im of the school of thought that anything that can break eventually will and if your belt breaks you're pretty much SOL. If your chain breaks you remove the broken link with a cheap chain breaker, pop a new one in and keep going. No biggie. Plus a chain lets you play with ratios. Theres no one that we are aware of that makes a pulley that will work as an aftermarket part for our beloved savages.
The oil leak sounds like the head plug as verslagen suggested. The fix is well documented and cheap. It just takes a little effort and some RTV. Keep a close eye on the oil level until you get that fixed. My leak was so bad I'd lose about 1mL a mile if I was going anything over 40mph. Overfilling on these machines isnt an issue and that makes oil checks a lot easier. Screw what the manual says, leave the bike on the kickstand on level ground and fill'er up until the oil reaches the bottom line on the window.

      Sometime ago there was someone on here that had 44,000 miles on the belt and it was still fine. I guess there can be a lot of variables...........