Do you have a check-valve in-line with the line to your tank/booster and is it installed in the right direction? This helps store vacuum at higher levels, during decceleration, for example, so that you have it available at idle. I run a similar cam and usually have no problem unless I have to use the brakes several times in a row at low idle.
I was told to keep the idle up at 1000 to 1100 to "keep
oil up on the cam" so you may want to run a little faster idle, which will probably also give you a little more vacuum.
Low idle speeds are a can and should. You can idle it at 800 but you probably shouldn't. Of course, others will dispute this so take it for what its worth. Of course, now that I re-read, I see that you have a hyd roller, which eliminates the need for
oil as opposed to a flat-tappet cam. The higher idle will still help with vacuum, though.
Gary