You should look at the following considerations before upgrading.
1.Is it a 3G unit? Battery drains faster because of the "in your fingertips" kind of user interface. With 3G connectivity on in iOS5.1 vs.4.2, the battery mileage will decrease faster than those of Wi-Fi units
2.Are you having preference of things like "notification centre", lock screen changes, iCloud etc over battery performance? The difference in battery performance differs from user to user. It's the way iOS5 is built that lowers battery performance.
3.How often are you close to a wall socket OR how willing are you in using an iPad while its bound by a cord?
There's no turning back.
4. Possible performance degradation - read around the iPad forums. It may happen.
The question is, would you go for acessibility and convenience to an extent that battery performance/hardware performance is compensated? If you have already given it a thought, great.
You need at least Windows XP to download the latest iTunes which is capable of upgrading your iPad to iOS 5.
The link in your discussion should also aid you in the consideration.
iPad: Which iOS 5 features does my iPad support?