I have been using Win LP primers in the 45LC (250XTP) and 480R (325) with 25 grains of H110 since day one and have had zero problems.
If you read up on the Win LP primers you'll see they are designed as a dual purpose primer good for std and mag loads which is why Win dosn't mag a LP Mag primer.
As far as everything else goes if you look at load books that are detailed and show multiple powders and charges for a specific cartridge and H110/W296 is on the list in the footnotes it will tell you to use mag primers and the primary reason for that is the load density common with those powders and reliable ignition of the charge. Just changing brands between primers can change pressure and according to one test I read about the pressure changes were up to 6000psi so when you go back and fourth there will be changes in velocity and accuracy no matter how small. Back to the load manual deal, I was cooking up some hot loads for my 44spcl the other day and every place I actually found the data I was looking for would say to use LP primers "except" with H110 and 296. Something else to take into cosideration, the tests ballisticians do to give you that information came after hours of testing in all kinds of cartridges, weapons and environmental factors. A good example is that common sense says that most likely a compressed case of H110 is going to ignite more easily on a warm spring to hot summer day when most of the armchair ballisticians including myself to an extent are shooting but what happens when the temp drops to below freezing? Will the standard primer still be as reliable and as "consistant" as the mag primer in ignition? Anyways I find it much safer and better to trust the guys getting paid to do the proper testing and research on the matter.