Why not go for the 4% IAS and 1-12 lightning?
Anyhow, you can just create the HOWA's in PoB after importing your character and setting up the skills, then you can see the actual DPS increase. But yes, it makes a lot of difference when it comes to the actual numbers.
However - 3 months in, league would be over, at this point everyone is one-shotting everything and the dps difference of 200k vs 300k in the tooltip isnt something that you really feel ingame.
What I do wonder when it comes to monks tho, wouldnt you get a bit higher dps at 275 dex and lowering int a bit? At least that was the case for my deadeye. And I had 1-12 lightning on my Howa's but lacked IAS% on my gear, so the breakpoint for me was at 275 dex.