4350 with the 30-06... any flavor 4350 will do, but I use I 4350 in every 30-06 I put 165's through, including my current 30-06... wlr or a mag primer and work up from low 50 grs with book data... I usually land between 56 and 57 grains I 4350 with a hornady pill...
Your 243 will sing a pretty song with any 70-75 gr pill with I 4064... I have used around 40gr with a 70 speer tnt in a few rifles now and it has been great... The speer and hdy 75's are no different there; the remmy pill shouldn't be any different... the 243 will do well with a fed 210 or cci 200 with a powder like 4064... I or H 4895 would be decent too...