Is it coincidence that you got to #311 in your Mantle quest and figured you've gone enough?
I think it would be a great quest. Getting the Ryan cards are simple enough especially without high grade requirements. Having the 68 helps as well. Ryan has been such a great signer for so long I think it's tough enough to be a challenge but not so tough you might break the bank or get stuck.
If you come close and find a handful still needed he will sign TTM through his company. It takes a while to get back but the price isn't outrageous compared to others his caliber and some proceeds go to his charity. Sound like a win, win.
Best of luck and if you attempt you should keep a running post so we can all share in your excitement.
Drew
Ps. Sorry about the thumbs down on top of my post. I don't know how I put it there or how to take it off.