Hmm, there isn't much to change in your cfg (btw, some of the values you have ar enot allowed in etpro servers, but I guess you don't play that mod)

you have:
com_maxfps 60 (set to 125, otherwise you won't get more than 60...)
r_ignorefastpath 1 (0 is faster)
r_lodbias 2 (a low value means more details, try something like 7)
r_lodcurveerror 250 (250 is default, try 60)
snaps 40 (set it to 20, 40 makes no sense at all, because all servers run at 20fps and asking for 40 is stupid, at most you can get some duplicate useless frames and waste bandwidth)

other things for more fps or better gameplay:
cg_coronas 0
cg_atmosphericeffects 0
cg_bloodtime 0
cg_bloodflash 0

If you play in servers with punkbuster you can try this:
pb_system 0 // you can try 1 as well, 0 is the one I use
pb_security 0
pb_sleep 500
pb_writecfg

And check if other processes are using your cpu or harddrive while you play, use process explorer, or any other software that shows you per-process cpu usage, and io history graphs.

If you play in servers with big open maps and too many players, it's normal to have some fps drops, but 50 is a bit too low. I get 50 sometimes, but my cpu is slower than yours.

p.s.
you say that cod4 takes more resources than et, I don't know how you checked this or you are just guessing it, but if it was true then you would have more fps in et than cod. If you have less in et it means et needs more resources than cod.