@both, considering my opponent is 1800+, I think he'll choose the best move, that is Ra1 - attacking my weakness.
I would love to trade Queens here and just stomps up the Queen-side with my pawns march, but I doubt he would allow a Queen exchange.
Depending on your next move, his next move probably gonna be a1. And then you probably would move to b7. Then he might move to d7, and then you probably move to b2. And then... stuffs... >__>
I think the best move for me here is 40. ... b4, anticipating Ra1 (as you pointed out).
Since my opponent has a Rook and a Queen, it is important for me to keep the position closed with my Bishop, Queen and Pawns.
This is to avoid their penetration into my position since my King is only "relatively" save.
One variation I have in mind after 40. ... b4;
41. Ra1 Qc4 (keeping the position closed).
If I'm able to exchange Queens, then I should win easily.
Bishop to C4 wait for his move
Then he'll move 41. Ra1..., and I need to defend my a6 pawn.
41 ... b4 is the only reply, but now his Queen can penetrate deep into my position with 42. Qd8 ..., threatening 43. Qf6+ and all my King-side pawns structure will fall apart.
What do you guys think?