The memory footprint of all but HDC are small. The disk IO which is the part that stops the actual crunching, because it happens at a higher priority, is when running very large models of 1gb+ and Virtual Memory or Checkpoint saves take place. Defragmenting the disk and using the PageDefrag utility to be run at boot time (once or every time), can reduce much of the slow down. If still suffering, you can de-select HDC.

A New option in the BOINC 5.8.8, just released is the 'use memory while busy and 'use memory when idle'. The default is 50% busy / 90% idle. It would simply put the HDC job in a 'waiting to run' state and start the next job. With a mix of FAAH and HDC the next one is very likely a FAAH job.

The above noted options are not yet all accessible thru the website or thru BOINC preference controls, so have to be put manually in an text file called global_prefs_override.xml

<global_preferences>
   <run_on_batteries>0</run_on_batteries>
   <leave_apps_in_memory>1</leave_apps_in_memory>
   <max_cpus>1</max_cpus>
   <disk_interval>999.000000</disk_interval>
   <ram_max_used_busy_pct>60.000000</ram_max_used_busy_pct>
   <ram_max_used_idle_pct>90.000000</ram_max_used_idle_pct>
   <cpu_usage_limit>100.000000</cpu_usage_limit>
</global_preferences>

Lines explained in brief:

Batteries: 0 means not to run on battery.
Leave in memory: 1 makes that project switching goes without crunching loss, though checkpoint switching is better in 5.8.8
Max CPUS: 1 on a dual core machine 1 would only use half the crunch capacity. Don't know what a T60 has.
Disk interval: 999 seconds keeps the model for 18 minutes without writing to disk unless a checkpoint is found.
ram.... busy: 60 the important one is my choice on a 1.5gb ram machine
ram.... idle: 90 is the default and leaves some for other processes.

Will post if i find a file explaining them all in detail.

When saving the file to the BOINC dir, make sure to save it with the xml extension and not txt. Else just rename it an file manager.

5.8.8 for Linux is not gold at time of this writing, but for MAC and Windows it is!

I've had to give up on HDC. It's just too big and too painful to run in background on my machine (T43, 1GB Memory 2GB swap file minimum).
I become VERY conscious of when HDC is running and have had to remove it from my possible projects as, even when it's running at idle priority, it pushes me up well beyond physical memory and EVERYTHING swaps too painfully to get work done.
Sorry HDC developers, but, unless you make the footprint similar to other projects, I can't help participate in the research.

i have a t41, no problems at all.