I voted for the 40% miss option. I feel against a evenly matched foe you should hit almost as often as you miss, but missing just isn't as fun and exciting so should be a bit less likely.
And as for the anti-climatic critical, In my gaming experience these can often be far from anti-climatic. In one game I ran the PCs encountered the campaign ending big fight against their long standing nemesis. The enemy was far more powerful than any of them, prepared, invisible, flying, and casting instant death spells at the PCs. The fight went 2 rounds, round 1 bad guy cast instant death spell on party member, party member resists partially and bleeds from his pores - the party starts to look for the bad guy. Round 2 the bad guy cast instant death spell on PC member, PC resists partially - his heart momentarily stops but returns to beating - another PC crits his perception roll and finds where the caster is, crits his attack, rolls location (head shot).
Rather than fudge it to make the fight drag out longer I just let it go. The player shouted, laughed, and cheered for a half hour afterwords. We wrapped that game up early it is true, but we had plenty of fun anyway. They still talk about that fight to this day. I suspect GMs are more let down by these kinds of "anti-climatic" fights than most players are.
On the other hand, I do tend to avoid instant death effects in most games to avoid this issue against the PCs. The above example was an exception that made the fight stand out all the more. When the PCs know that instant death attacks are rare but start seeing them, they typically react dramatically. When instant death attacks are just uncommon, they tend to consider them inevitable.
-Pyrotech
