Good for you. I just did a quick test of the mini 2 (ios 10) and mini 4 and 5 (ios 11) for browsing. The mini 2 opens pages fast enough, but scrolling is so slow I have to wait for the page to load every time and it stutters. Also selecting text is slower and sometimes makes it stutter. The mini 4 feels much more similar to the mini 5, scrolling is fine and I find it perfectly usable. Honestly the main reason I upgraded to the 5 is for pen and LTE (my mini 4 was wifi only), not so much for speed.
Having said that if you only use your mini 2 for simple browsing (not selecting, copying, pasting, TTS, etc.) it's tolerable but as soon as you start using Office, PDFs or simply open several different apps, you have too keep waiting 5-10 seconds every time you open something with some occasional freezes and crashes... which for me is a no go