Between RC5 and GF, RC5 is slightly better on a Celeron, as you can see from my Opportunity Cost table:
OC ...... Processor
Better at RC5
6.52 .... Cyrix 6x86
6.77 .... Cyrix 5x86
7.35 .... 486
7.59 .... Ppro/P2/P3/Celeron?
8.10 .... Pentium MMX
8.24 .... Athlon
9.41 .... K6
11.18 .... K6-2
11.18 .... K6-3
11.43 .... Pentium
Better at GF
8.77 .... Average
RC5/OGR is kind of a toss-up for Celerons. About the only thing they don't do well is SETI.