A little late, but let me drop my 35 cents.
I downgraded a spare iphone 4 from 6.1.3 to 4.3.3, as i realized that cydia had saved my 4.3.3 blobs when i first jailbreaked, some 2 years ago.
And let me tell you... i forgot how fast this phone used to be. I found some old ipa files i did backups of (facebook, messenger, ibooks, some games etc) and it runs like a charm. Facebook had become unusable from the recent updates. The only things i miss are the notification center and the lack of a few usefull apps for which i've been unable to find old versions of. Oh, and the native ipod and phone apps are miles ahead (speaking in terms of design); they just fit the rest of the os just perfect. Why oh why did they have to change 'em...
So my advice is the same as the one the guy ahead of me gave you: stay at all cost !
PS: And all jokes aside, Safari IS way faster.