Yeah I was thinking a 3rd party site would be best for something like this anyway. I don't really have the programming skills, myself. I could set something like this up on a Microsoft Excel workbook, calculated manually but not on a website. Perhaps the best way to approach this would be for me to calculate it manually and post it up here on Steemit once a week or so, and then if someone with the programming know-how likes it, they might choose to recreate it on a 3rd party site.
What I'm thinking of is something like a calculator that really spoon-feeds a new user the bottom-line data they need to pick a project. Each 1,000 RAC on "X" project is currently worth 15 Magnitude, which translates into 5.52 GRC per day.
From there it would be super simple to browse through the userlist on the GridCoin team and find someone with similar hardware to see what their RAC is to estimate what you might be able to earn.
PrimeGrid is a great example. There are actually quite a few users on that project so when you look at the Project list on GridCoinStats.eu, it's not the first project you're going to pick. It turns out the competition in that project really isn't very high, though, and it's pretty easy for a single GTX 1070 to yield you a 200 Mag or so (currently).
I'll think about how I could set something like that up to spit out here on Steemit. That way when we get that question on Reddit, we can just link people to the most recent article on this site.
Primegrid is a special case. PPS Sieve is awarding more credits than other subprojects because you can't actually discover new primes when running PPS Sieve (you are doing some sort of "preparation work", check here for more details).
When running other GPU Primegrid subprojects (GFN), you can actually discover new prime-numbers pretty quickly and you get some recognition for that, so Primegrid admins decided that's already a big enough incentive and reduced the credits awarded for GFN (while increasing them for PPS Sieve).
The point is, any "rewards calculator" can be quite tricky to implement, since it will require in-depth knowledge of every BOINC project and they are bound to get more complex with time. In this case, it wouldn't be enough to point users to Primegrid, they would crunch GFN, earn mediocre credits and get disappointed. They must be pointed specifically to PPS Sieve, if you are promising big rewards to them.
P.S. I am a long-time Primegrid cruncher, got all this info by following their message boards for years, it isn't readily available anywhere else, as far as I know. BOINC admins can fine-tune credit reward system as they see fit, for every project and subproject. Perhaps WUProp can provide necessary correlation.