lost my top speed on my cbr

Hey i recently had a slow speed crash (about 20 mph) on my CBR-125 hit some oil and just slipped and hit the side, everything was fine just steering was off abit so sent it in to get my steering fixed and MOT’d and they said everything is fine.

I then noticed a lil while later that i had a lack of power i checked my bike and realised that id been lazy with my chain checks (slacker i know) so i tightened my chain and up to 4th gear my power is now fine, but as soon as i get into the top end of 4th gear i just loose power.

My realistic top speed has gone from 75-60ish. Also (quite weirdly) my gears seem to be covering a higher range of speeds. it used to go up to go

1-20(1st) 20-30(2nd) 30-40(3rd) 40-50(4th) 50-60(5th) 60-75(6th)

but now i can get up to 45 in 3rd, and up to 55 in 4th, i know thats not a big change but once i go into 5th i get no extra speed just less vibration and as soon as i hit 60 my revs go down to 6-7,000 and i slowly slow down untill i get to about 55.

I have no idea whats doing this the crash was just cosmetic damage and the off steering.

Any ideas? Thanks.