-Load a large xrns (100ish patterns for instance) and try and cut for example patterns 2 - 7 via the right menu/ ctrl-x
in renoise 2.1 this will be instant where the same song loaded in 2.5 (b6) needs some thinking time, maybe 7 or 8 seconds for exactly the same task?
in 2.5 (b6) these cut operations seem faster at the bottom of the sequence, cutting 93-97 would be almost instant in this case.
Testing this was using directsound drivers at the same latency
I can confirm this!
This is probably because of the MIDI assignable matrix cells.
I think this will go 2x faster than B6 if you try the same trick in B5.
Taktik already said something about he would deal with the MIDI map matrix slowing down loading stuff, that might include automatically fixing this one perhaps.
I shall wait and see then. b5 lives on my machine no-more…
Not that I don’t think this should be optimized, but holy-smoly 100 patterns? Of what length at what speed? 
I tend to keep a lot of discarded patterns when working on a tune and sometimes go back to / re-arrange etc.
So not as epic as it may sound, but might explain why I need the cut operations here