Regardless of what you read (here, or otherwise), jailbreaking does not make your phone "horribly slow."
There are some themes that do, but "horribly slow" is not an inherent side-effect of jailbreaking.
You can still update your OS, but if you do, you will lose your jailbreak, and you will need to do it again if you want it, but you do not have to.
Aside from jailbreaking, the only way to tether your laptop, is with NetShare, and it has been booted from the app store.