First what I know: I have installed two OTA updates on my Austria sourced Note and aside from the slightly modified standard keyboard I cannot say that I have noticed much.
Next what I am speculating: I would say that, unless you have a hardware problem with your antenna, you probably have more of a signal problem that a firmware one. Do you haven't 4 bars of signal when this is happening or are you barely connected? The H and H+ data rates are negotiated on top of the 3G signal so you need to have a good connection to get them. Do you have the problem everywhere or just in one location? Do you also lock your Internet connection when using WiFi?
Not much help so far but I hope that this gives you some pointers.