Whichever one provides the greatest benefit will override the other.
So, no, they do not stack.
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"God created man from a handful of dust, and he created woman from that man's rib. And these two together were so stupid that they weren't on the planet five minutes when they managed to get a curse put on all future generations. Nice work." Pat Condell
I've heard you have to be 55 to do the combines, but I can't confirm this. I've also heard that you have to be flagged for a 3rd tier zone, but this is not true. I got mine at 58 and only flagged for CoD. Hope this helps.
The way item focus effect stacking works is whichever one is better in a given situation, is the one that takes effect. Chromosphere is better than MP IV but it only works on Sun Vortex, so Sun Vortex gets the 25% savings from Chromosphere and everything else gets the lesser savings from MP IV. So having both items is NOT a waste, unless for some reason sun vortex is the only spell you cast and I think that rather unlikely. ;)
Interesting how melee haste works the same no matter which weapon you're using. Be interesting if there were superior haste items which only work on a specific class of weapons like 2hb or piercing.
Edited, Thu Jul 31 14:22:04 2003
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Sage Artulyn Starsummoner 105 Archmage of Omani Winter on Bertoxxulous For the Light of a Candle to be Seen, It must be taken to a Dark Place -- UKLG