Periwinkle or myrtle, if they are the same, is one of the most aggressive and undestructable plants. I have tons of it and would get rid of it, if I could. It has a brief show of violet-blue flowers in Spring.
Epimediums, on the other hand, will also exclude most weeds and seem to fend off the myrtle. Flowering is brief but there are many color choices. I cannot imagine having too much of it. Unfortunately, they are not cheap to buy.
The only negative is that I must string trim down my Epimediums, this time of year, as they look really bad.I do this, also, to make the flowers more prominent. The myrtle or periwinkle continues looking fine.

I think I'm talking about the same plant - but call it "Vinca". I love it! I live on a rural five acres and have been doing naturalized landscaping for thirty years trying to reclaim a "worthless" piece of property that is now incredible beautiful. Someone gave me some garbage bags filled wiyh Vinca they were throwing out. I planted it in steep ravines where nothing else could grow. They are gorgeous now!