This is a very tough guess, especially with a pickup pard.
You are most likely down 2 in 5H vs. their making game, which is a small gain (4 imps). When they are going down, you lose 7 or 12 imps depending. You could also be down 3 vs. their game, which is lose 4.
You basically only make if partner has a heart void (maybe 50%) and an Ace (~10%?) or crazy shape. Then you gain somewhere between 11 - 16 depending.
Partner should have some outside strength vulnerable, and you may be able to negotiate a club ruff.
Assuming they are like 80% to make their game, and you are 5% to make yours, it's almost dead even from an imps perspective.
Good problem. I think it's a toss-up. I'd guess to pass, but wouldn't criticize a bid. If I didn't think my LHO was a good player, I'd be more likely to pass, as this could be a very tricky contract.