Yesterday I disabled a few widgets:

personal ip
ap news
conversation inbox
fm transmitter on/off

and restarted the phone and have to say that it feels much snappier and has stayed that way. I opened a lot of browser windows last night & also listened to music & checked emails. I left most of the windows open overnight and kept on using it this morning and though it slows down a bit when doing too many things, music playback has been much smoother than before and swapping between windows is still quite fast.

If things keep up like this I'll certainly be much happier but I'm gonna give it a few days since reproducability is one of the main problems with these slowdowns.

Thanks for the advice!