Okay....updated graphics card to ATI Radeon 5770 & a NEC PA242W monitor.
LR6 reads the GLU interface 5770 card - not yet sure whether LR is taking advantage of it in the Develop module, but editing is not any slower than prior with the GeForce 8800 card - so perhaps all is good.
The NEC is very nice, calibrated the display with Spyder 5 Pro and it seems better than the Apple Cinema display (but of course $$$ spent and physiological pleasure !), using AdobeRGB, not used NEC's calibration software as of yet. All seems good. May look into anything else I can do to enhance WISIWIG - but my prints look good from screen to print.
Not sure I wish to play with Radeon card of NEC drivers at this point as all is working well.
Perhaps there may be a fine point in tuning here and there, but then......time versus fun!!!
So, thanks to everyone for input....
aj
hello Aj, i have the same 2008 computer and am still working fine on it.
I also upgraded mine and think you can only add a system SSD to make it work faster, considering what you have done till now.
It does not have to be 1gb , my guess is 256 GB is enough, but some have loads of music on it , so i could be wrong. ( you could put the music on an other drive though)
it will cost you only 100$ and it will be something you will clearly notice - unlike the graphics card ;
BTW i would have suggested an other graphics card ( or non at all) , the ATI 7950 or 7970 since they support Metal-accelaration in El capitan...and have 3g of ram.
For printing you do not need a better GPU than what you had; but the screen will be a step forward i am sure...
(More ram is only needed if you can see in the activity monitor that you do not have enough for your kind of work)