With lipo:
The good: Battery weight will be well under half of what the lead acid weighed. You will also see a performance gain from the massively reduced levels of voltage sag.
Also, lithium batteries give you ALL of the usable aH whereas in a high amp draw situation with lead acid, you only get 1/2 - 3/4 of the actual battery capacity, so 5ah might give you the same range... or maybe even more range.
The bad: you will need a balancing charger, especially with that small amount of battery capacity. It will need to be balance charged often as the cells will get out of wack at the bottom of their charge ( which they will be at often, it sounds like. )
You will have to break apart the pack to balance it each time. Although i think a new hyperion charger that does 14s can help you get around that. To be at the stock voltage, you'll need a 13s pack, so that would be ideal.
so in essence, more charging hassle than lead acid for sure.. but massively reduced weight and improved performance.