No, in the case of UT3 and many other such apps, when they say 2.4 or 2400, they mean that in the sense of the older P4 ways... Pentium based 2.4Ghz or AMD based 2400... The AMDs are much more efficient than the Pentium 4 and below.
Had they meant that it needs a 2.4Ghz CPU, WTF would that mean for Core2Duos ?? - they are more than twice as efficient than the P4s are.
No, an AMD x2 3800, this is more than enough for UT3.
In my honest opinion, clocking the CPU is not the answer in this case... Sure, it will make the CPU a tad nippier, but thats all it will do.
I would accept the system AS-IS, and leave it alone and consider the Intel path.
Although, my No.2 PC went from an X2 3800, through an Opteron 175 and on to an E2180 and to be quite honest with you, its not playing games any better... Not really.
I think I was happier when it was the opteron and Im still 50-50 on going back to the Opty for My No.2 system.
I still have my Q6600 as my no1 of course and there is no way I would be stupid enough to go back to AMD at this time because no AMD on the plantet is as quick, but that will change soon probably.