I've played with Obligattos, Dominants and Evah P's for about 10 years. I found that all perlon core strings only have about a 10 month life span and then they suddenly die. I think when certain percentage of little strands inside break and dirt gets in through the windings, the string loses it good tone.
Since switching to Spiro mittel G, D and A and a stark E, I've been much happier with my sound and playability. I play about 90% arco and 10% pizz.
Also, giving your perlon core strings a good deep cleaning to get the dirt out from between the windings will give you another 2 or 3 months of good tone. (Loosen string, use methyl hydrate on a face cloth and run it up and down the string while bending the string into an "S" shape around your fingers. Keep doing it until no more black appears on the cloth. Retighten string and go on to the next one.)