As palo and Bubble say, both 4895s are a bit fast burning for heavier bullets in .243 Win. As to Hodgdon v IMR differences, both come in reloading form from the Hodgdon Powder Co. of Kansas USA and to us via its importer Edgar Brothers in Macclesfield. They are not the same powder although they have similar burning speeds and do the same jobs.
IMR (Improved Military Rifle) is the original version developed for the standard US military loading of the 150gn FMJ .30-06 ball round pre WW2 and manufactured in the USA by DuPont for generations. For Health & Safety reasons and the associated costs, manufacture moved to the IMR Powder Company in Canada some time back and which has since been bought out by Hodgdon.
The Hodgdon version is manufactured in bulk by the former ADI (Australian Defence Industries, the privatised Aussie arms and ammunition manufacturer, ship repairer etc) now part of the huge multinational Thales defence, transport and manufacturing group.
H4895 has shorter grains than the IMR version and like nearly all Hodgdon extruded powders is nearly temperature insensitive. There can be differences in recommended maximum loads between them and the IMR stuff is a little bulkier so might fill a case better - or take up too much room. Both are available here, but the Hodgdon version is much more common and is stocked by most shops that do handloading supplies.
Thales Australia Ltd does an ADI Handloading Guide that is worth downloading by people who use Hodgdon powders as it provides loads data for cartridges and some combinations not covered by Hodgdon's data.
http://www.adi-limited.com/handloaders-guide/
The powders that we get here are:
AR2205 = H4227
AR2207 = H4198
AR2219 = H322
Bench Mark 2 = Hodgdon Benchmark
AR2206H = H4895
AR2208 = VarGet
AR2209 = H4350
AR2213 = H4831
AR2217 = H1000
AR2225 = Retumbo
AR2218 = H50BMG