Today I got asked "If you had 4 x lvl 5 health gems (20% bonus each), would you embed the four into different items or craft one lvl 6 gem?" By the way a level 6 gem is 25% bonus.
I would say it depends on how many pieces of gear you are planning on crafting in the near future. For example, if you are reaching hero level 50 soon, then keep them as four separate gems because you are going to be crafting a bunch of new gear.
If you are like 46-48 and it's going to take you months to reach 50 and you are just going to craft a high level chalice or odyssey than go ahead and put a level 6 gem in there.
Although, I really think 90% of the time you shouldn't combine them because you should be making at least one piece of gear every month or two. For the record I have no level 6 gems, although I don't remember if I had the opportunity to make a lvl 6 gem at the time I was embedding.
The most important thing to me is that I have a full set of battle gear with the highest level and most applicable gems in every spot.
All spenders should wait for level 6 gems if they don't already have them. Spenders shouldn't have a hard time getting
level 6s unless they trying to get rare gems like Rose and Boar.
Enjoy!
Navi