@biffyclanger afraid not. The 5 APR from MMM is the maximum from base attacks and the additional 1 to base that offensive spin grants is therefore disregarded. You can get 6 APR though if you use haste.
6 apr can be achieved without haste or improved haste. A level 11 priest of lathander gets two uses of boon. Boon definitely does stack (I run this build on my favorite character android bg2ee) and it also breaches the 5 apr limit. Dual to a ranger at 11. At 13 the ranger can get 4 apr with any weapons a cleric can use if he dual wields, weapon specializes, and uses the extra 1/2apr gloves. Cast two back to back boons and for a few rounds enjoy unhasted 6 apr with crom, or flail of ages, or whatever you want, cleric-wise. Also ring of gaxx doubles the boon attacks so with just one cast of boon and imp haste from ring you can have a 10 apr cleric. Overpowered? Absolutely!
Mods can go even higher. With one of the Sword Dancer kits from Expanded Classes and Kits, you can hit up to 30 attacks per round. The Sword Dancer kits make three attack rolls for each attack, which stacks with (improved) haste, though they only deal 1/5 physical damage to compensate.
Also, the Scorcher Ammunition strikes twice with each attack roll and grants 5 base APR, which allows a regular fighter to strike 20 times per round under either GWW or Improved Haste. A Sword Dancer with the Scorcher Ammunition could strike 60 times per round.
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Also, the Scorcher Ammunition strikes twice with each attack roll and grants 5 base APR, which allows a regular fighter to strike 20 times per round under either GWW or Improved Haste. A Sword Dancer with the Scorcher Ammunition could strike 60 times per round.