Ive toured with rear load only (prob about 30lbs), four panniers with really small front panniers and more weight at back (essentially 1980s racks and bike, so kinda loosey goosey), and four panniers with more weight up front in front panniers (with a good solid front rack and fork)

I've really come to find that I prefer how the bike rides and handles with four panniers and more weight up front (I really like a good handling bike going around corners or hoofing it down a downhill)
The main upside is that its just plain easier to pack stuff in four panniers, and so much easier at the end of day to throw groceries for the night and morning (and some lunch) into panniers and arent stuffed to the gills--a real possibility with rear panniers only, as mentioned, especially with extra food and water.

also, some panniers weigh a lot more than others, so look into pannier weights also, just as you would with tents, sleeping mats, sleeping bags etc

in the end, try it out and see how things feel--just remember that extra space is just plain darn handy for throwing in food bought in stores.

heres a photo of a recent overnighter I did, I could have just used rear panniers, but like I said, its just easier using my tried and true methods of putting X stuff in X pannier, and Y stuff in Y pannier like I've done on numerous longer trips over the last 5 years or so.
My bike looks heavily loaded, but it isnt, total gear weight was about right at 30lbs, and the bike handles really well like this, which I appreciate especially when riding fast over loose surfaces, which I did at times on this trip.

ps, the rear pannier you see has my tent poles thrown in diagonally in it, easier to strap down my tent on rear rack tightly due to rough roads (didnt want to risk bending poles) so it makes the pannier look heavy and full of junk, it wasnt heavy at all.