Well the fact that the .303 Lee Enfield rifle is still in service across the world speaks for itself. In some armies across the world it is still a designated sniper/marksman rifle, it is also one of the largest privately owned rifles in the world.
It featured a 10 round magazine where as the KAR 98K held 5. During WWI British and Commonwealth forces in rifle companies could put down enough fire from their .303's that sometimes the German forces they were engaging were under the mistaken belief that they were up against a machine gun. If you're interested look up on you tube ".303 Lee Enfiled mad minute". Basically this involved upwards of 20 aimed rounds a minute, with some reports stating 20-30 rounds a minute. The video actually shows a British Paratroop re-enactor firing the rifle at a very fast rate for a bolt action rifle.
The KAR 98K (along with the MP-44, FG-42 and MG36/42) were quite extensively used in Vietnam by Vietcong forces. The Vietcong were supplied by the Soviet Union at the time and because of Soviet Russia's involvement in the eastern front which brought about the collapse and surrender of Nazi Germany, they had a surplus of German weapons which along with the AK-47 were supplied to the Vietnamese. This was also the case with the earlier Korean war.
I have fired a .303 myself, in both .303 and a rechambered .22 version. I have not fired a KAR 98. The range i was on at the time was about 200 meteres, when i got used to the kick of the rifle i was hitting the target with a very good grouping. Personally, as a Brit i'd go for the .303.
Hope this helps.