For you guys who have had experience loading Hornady 220RN and IMR 4350 with various brass cases.  What have you noticed about using different cases with a given load?  I am working my way up from 38 grs of IMR 4350 using Remington cases.   I was in the +/-1800 ft/ sec @ 38 grs.  At 39 grs I was getting more like 1915 ft/ sec.  I came up with a variety of Winchester cases and some relatively recent, others older, and some even older 1950's Winchester super speed cases.  They weigh more than the Remingtons do.   In general, how different are your loads?
Also, given that I am around 1915 ft/ sec @ 19 grs of IMR 4350, will 40 grs and being a little over 2000 ft/ sec be any issue?  (Model 1898 with a very nice full length barrel)
Thanks.