unless you are adding more machines to your mix, you have forgotten a couple of  details.
I am going to add another HT machine of my own in the 30-60 days. That should add an RAC of 600-800 (todays numbers)to the mix
It isn't that I have forgotten it, it is that at this point there are too many variables to take into account.  
1/ My RAC is not stabilized yet. (Currently listed as 604.25 but over the last 6 days my total has gone up by 6300 - 6300/6=1050)
2/ When/if you add the additional machine, its actual RAC, how much control you have over it.
3/ I've been toying with putting together an Athlon X2 myself and that would be a major boost to my RAC as well. 
 
 Seti is going to switch to the enhanced client in the next few weeks. WU's will take 4-10X longer to crunch. WU's will have deadline measured in months instead of days. It could take up to 3 months to get credit if 1 person is slow in crunching and returning
Considering that SETI 1 going offline soon was over 2 years I am not going to worry too much over the "enhanced client".  Also unless they abandon the existing concept of cobblestones then a WU taking longer will just mean more credit/WU so no change.  It might cost you some credit yourself, will your two slow machines still be useful if WUs take 4-10X times longer?
PS, how about unhiding your farm so I can really see what I need to do to stay on top.
My little farm.  
Date activated Recent average credit     Total credit     # of CPUs    CPU type                     CPU SpeedDec 19th               191.14                     3,423.65           2            Athlon(TM) MP 2100+    1.733ghz
Dec 23rd               151.54                     1,988.57           1            Athlon(tm) XP 3200+     2.2ghz
Dec 23rd               157.19                     2,052.79           1            Turion(tm) 64 ML-34      1.8ghz
Dec 26th               152.39                     2,056.65           2            Athlon(TM) MP 2400+    2.0ghz
Total                  ~
652  Remember my RACs are still increasing though the first machine should stabilize soon.
I passed Cyberkada on the 1st and SlackerJoe last night putting me in 8th for total output.  
5 ) AJTK            26,323.40   247.85  United States
6 ) f9TH SIR X    20,909.17     9.85  New Zealand
7 ) KD4             11,050.56    11.84  United States
8 ) IKV Nemesis   9,585.73   602.26  Canada9 ) SlackerJoe       9,350.29    11.06  United States
10) Putanginamo  8,687.99    65.43  Philippines
KD4 should be hehind me Tuesday night then it will take a while to pass f9TH SIR X as that gap is bigger.