I'm spitballing and brainstorming, so don't jump down my throat if I'm off the mark, but here goes!
It's kind of like saying "Which is healthier, apples or oranges?"
They share a lot of common vitamins and all, but they're different fruits, so they'll be giving different advantages and disadvantages too.
So, compare warmth, but also consider the following:
The Ibex has thumb loops, which might save you weight on gloves.
The Ibex is Merino Wool, which has been tested and proven to smell significantly better after long-term use and prevent bacterial growth.
The Ibex makes a good baselayer in sub-40ºF conditions
Weight Savings, that's a biggie.
The synthetic fleece is thicker, which takes longer to dry and won't move moisture as efficiently.
So, you'll save a lot of weight going with the Capilene. However, if you replace your baselayer with the Ibex instead, you'll gain a next-to-skin layer that will deal with your sweat much better. Additionally, you can supplement your hat and gloves easily with more thin wool. The Capilene can't really do the next-to-skin thing as well, since it won't wick and evaporate moisture as fast and it'll absorb sweat odors, which means you'll probably want a thin baselayer, which is more weight. Even if you don't... there's still that stink.
These pieces are different enough in purpose that a weight or warmth comparison isn't the whole story. if it helps, Andrew Skurka said his hooded merino wool baselayer with thumb loops was one of his favorite pieces on the Alaska-Yukon loop. The Ibex Indie specifically is his preferred piece for cold and wet conditions.