I had a non-silver OL RB-250 and found it worked extremely well with my Grado Sonata. It is extremely good value for the price. I never tried it with a MC cartridge.
I then upgraded to a Graham 2.2 with the .25mv output Graham Nightingale. That combination was a wonderful improvement to the RB-250/Grado, but certainly the law of diminishing returns clearly applied to that upgrade. I certainly couldn't swear that the improvements in my enjoyment of my records was worth the cost of the upgrade.
One thing I really do like about the Graham is how user friendly it is and how easy it is to adjust VTA. I would really have a problem going back to an arm like the OL250 where adjusting VTA is very difficult (or even worse, going back to a stock 250 that has no VTA adjustment).
It's not clear from your post if the 68db gain is exclusive to your phono preamp or also includes the gain of your preamp. If 68 db is your total gain, I think I would stay with .8mv output, but if you have another 10 or 20 db gain from your preamp, you can go as low as you want.
A good MC is generally an improvement over a MM, but I love the Grado cartridges and think they are better than a lot of the high priced MCs. In my experience, MCs just don't do well unless they are feeding into a step-up transformer. The first stage of my Rowland Cadence has a step-up transformer from Jensen, as does the ARC Reference phono pre-amp. However, this is a very controversial subject and others I'm sure will strongly disagree with me.
I then upgraded to a Graham 2.2 with the .25mv output Graham Nightingale. That combination was a wonderful improvement to the RB-250/Grado, but certainly the law of diminishing returns clearly applied to that upgrade. I certainly couldn't swear that the improvements in my enjoyment of my records was worth the cost of the upgrade.
One thing I really do like about the Graham is how user friendly it is and how easy it is to adjust VTA. I would really have a problem going back to an arm like the OL250 where adjusting VTA is very difficult (or even worse, going back to a stock 250 that has no VTA adjustment).
It's not clear from your post if the 68db gain is exclusive to your phono preamp or also includes the gain of your preamp. If 68 db is your total gain, I think I would stay with .8mv output, but if you have another 10 or 20 db gain from your preamp, you can go as low as you want.
A good MC is generally an improvement over a MM, but I love the Grado cartridges and think they are better than a lot of the high priced MCs. In my experience, MCs just don't do well unless they are feeding into a step-up transformer. The first stage of my Rowland Cadence has a step-up transformer from Jensen, as does the ARC Reference phono pre-amp. However, this is a very controversial subject and others I'm sure will strongly disagree with me.