375 Ruger is great
I had a BRNO 602 in 375 While living in South Africa (and also working for the South African NAtional parks for 7 years). Great calibre and rifle, but a very rough action. Hunted wildebeest, warthog, springbuck and one jackal with it. Very accurate for such a large rifle.
Today, being a reloader, and having access to the excellent Ruger bolt rifles (I own 22/77, 77MK11 VT, Hawkeye African, Compact Ruger Mag and a 458 Lott in the RSM configuration, Gunsite Scout), I can recommend these Ruger rifles to anybody. Smooth action (for a real 98 Mauser style rifle), good value for money and accurate enough as a hunting rifle.
The 375 Ruger is a great cartrigde if you want a short, handy rifle. In the 23" African or the shorter 20" Alaskan, this can be your one rifle does it all in America and Africa. It is not a tactical rifle, but then you can have a Ruger Gunsite Scout for that.
My next addition will be the Ruger Alaskan, also in 375 Ruger.
The magazine capacity in the old BRNO 602 and CZ 550 is more than the Ruger, but for hunting this is adequate. If you worked in Africa, and needed to cull buffalo or elephant (which ir urgently needed!!!), then a 5+1 mag could be a benefit. But then I suggest getting used to the reverse safety of the 602, or getting rid of it ! Obviously, ammo for the 375 H&H is very common, but is Africa the 375 Ruger is rapidly gaining momentum. Ammo here in Canada is cheaper for the Ruger.
Neither calibres will dissapoint you. Rather base your choise on the rifle / platform you wish to carry and use. Size does matter, especially after 10km of walking. I love my RSM in 458 Lott (very recent) but did not like the heavy RSM in 375 H&H, and rather selected a 375 Ruger Hawkeye African. ALso look at the new Winchester Alaskan (25"0 barrel, if you want to use open sights, need SS and Lam stock.
RSA = Reallife Shooting Application